Technical Report No. IRL 1105

CYTOCHEMICAL STUDIES OF PLANETARY MICROORGANISMS
EXPLORATIONS IN EXOBIOLOGY

Po
, . >
i a tay 2

Status Report Covering Period July 1, 1969 to J dauary 1, 1970
For

National Aeronautics and Space Administration

Grant NGR—05-020—004

  

Instrumentation Research Laboratory, Department of Genetics
Stanford University School of Medicine
Stanford, California 94305
Report to the National Aeronautics and Space Administration

"Cytochemical Studies of Planetary Microorganisms - Explorations in Exobiology"

NGR-05-020-004

Summary Report Covering Period July 1, 1969 to January 1, 1970

Instrumentation Research Laboratory, Department of Genetics
Stanford University School of Medicine

Stanford, California

Aoshua Lederberg
Principal Investigator

7 i N
oN eof Ogg bd)
lg AN Ok
oy, Or.
Elliott C. Levinthal, Director
Instrumentation Research Laboratory

Prtecre Ratan
A. INTRODUCTION

This status report covers the activities of the Instrumentation Research

Laboratory during the two quarter period from July 1, 1969 to January 1,
1970.

While the main support of the IRL activities during this period

continued to be the NASA grant NGR-05-020-004, some of the funds have
come from other grants, other agencies, and in some cases private
institutions. This report includes all the activities of the laboratory
which relate to or have benefited from NASA support regardless of whether

or not they have received direct support by this NASA grant.

We have sought support for our work from other agencies, particularly
the National Institutes of Health. We have had some degree of success,
especially in the area of cell separation. Effective January 1, 1970
essentially all of our work in this area will be supported by NIH grants
or contracts, GM 17367 and NIH 69-2064. We have received some support
for Dr. Halpern's work under NIH Grant AM 12797-01 and are seeking

additional support for his work on the interaction of chlorine compounds
with DNA,

These interrelationships benefit our NASA program in two ways. It aids
the rapid utilization for medicine and biology in general of the ideas
and skills developed because of our interests in space missions. It not
only provides us with the opportunity of testing instrumentation methods,
applicable to future NASA programs, in circumstances of solving current
scientific problems but also provides much needed additional support.
This support hopefully will permit the Instrumentation Research
Laboratory to continue to function with sufficient technological depth

and breadth to allow responses to future NASA needs.
For these reasons we have felt it desirable to carry out some laboratory
work that could lead to new fruitful relationships. A meeting on

Space Bioscience - Technology Utilization held on November 28-30, 1969
under the auspices of the Interdisciplinary Communication Program, was
attended by Professor Lederberg and Dr. Levinthal. This meeting
reinforced our conviction that there are areas of environmental health
that both make use of our scientific and technological skills and serve
our future possible interests. During this reporting period we have
expended some efforts investigating possibilities involving environmental

health in general and environmental health monitoring in particular.
The general areas of the program resume, Bart B of the report, are:

I. Optical Resolution by Gas Liquid Chromatography
II. Gas Chromatography of Amino Acids
III. Chiorine Reactions with DNA Compounds
IV. Apollo 11 Sample Analysis
Vv. Analysis of Natural Products by Mass Spectrometry
VI. DENDRAL
VII. Computer Aided Research Instrumentation
VIII. Cell Separation
Ik. Optical Data Processing
X. Quasi-Microscope
XI. Other Mission Activities
XII. Environmental Perspective

XIII. Reports, Publications and Papers
B. PROGRAM RESUME

I. Optical Resolution by Gas Liquid Chromatography

In continuation of our work on the g.l.c. separation of the D and L
antipodes of organic molecules via diastereoisomer formation, we have
applied this technique to the resolution of secondary alcohols, (4)
cyclic ketones, and phenoxyproprionic acids. Since the order of elution
of the diastereoisomers from a g.l.c. column is dependent on conforma-
tional influences the absolute configuration of the alcohols, ketones
and phenoxypropionic acids could also be established. The above
technique has also been applied successfully to determine the absolute
configuration of the allo-isoleucine which is present in the serum of

patients suffering from ''Maple Syrup" disease.

Il. Gas Chromatography of Amino Acids

Established methods for the g.l.c. analysis of amino acids involve

time consuming chemical manipulations to convert the amino acids into
volatile derivatives suitable for g.l.c. By using the injector port of
the gas chromatograph as a chemical reacter we have now succeeded in
converting the amino acids into volatile derivatives in situ. Since
this conversion was concentration dependent, the injector port of a
conventional gas chromatograph had to be modified to permit the removal
of the solvent, before the introduction of the sample into the heated
zone of the injection system. The simplicity of this process should

facilitate the whole operation.
III. Chlorine Reactions With DNA Compounds

Chlorine plays an indispensable role in the purification of our water
supplies and urban settlement would be imperiled without chlorination
or some equivalent means of removing polluting bacteria from water.
Despite our great dependence on the chlorine disinfection of water,
little is known about the mechanism by which chlorine kills bacteria.

It has been assumed that the toxic effect of "active chlorine" is
exerted through its reaction with cell membranes which are being
destroyed in the process, but since hypochlorite will also inactivate
certain viruses, other mechanisms must also be involved. The scanty
published data suggests that the most likely route involves an attack

of chlorine on the DNA of the microbe. This is supported by the
isolation of appreciable quantities of chlorinated cytosine and uracil
after hypochlorite treatment of Escherichia coli or tobacco mosaic virus
and the loss of infectivity of the virus subsequent to such treatment.
Additional evidence is also furnished by the mutagenic action of
5-halo-uracil, when it is incorporated into the DNA of bacteriophage T,-
Nevertheless chronic toxicity to man from chlorine has not been
considered a hazard because the chlorinating agent is known to react
rapidly with organics and the reagent is supposed to be destroyed in the
body fluids. This conclusion however ignores the. possibility that the
chlorine may react with a variety of nitrogen containing compounds to
form chloramines, which may themselves form potent chlorinating agents.
Although the bactericidal potency of known chloramines is considerably
less than hypochlorite itself, it is precisely the less reactive forms
of chlorine that makes these agents potentially the most insidious.
Whilst there is an extensive literature on the stable end products of
halogenation of the biologically important purine and pyrimidine bases
and their nucleosides and nucleotide derivatives, no serious attempt has
been made to look for, or characterize any of the labile chloramine
intermediates which may be present in these raction mixtures. This is

somewhat surprising, as the chemistry of structurally related nitrogen
heterocyclics suggests that fairly stable chloramine derivatives may be

formed.

In some preliminary experiments, we have been able to show, that the
action of sodium hypochlorite on the biologically interesting bases,

at a physiological pH, leads to chlorine containing derivatives which
behave as typical chloramines. These compounds give a positive color
test with tolidine (Von Arx-Neher) and liberate iodine from KI solution.
The latter reaction can be used to quantitatively estimate the amount

of labile chlorine present in the reaction mixtures. In the case of
cytosine, a crystalline chlorinated intermediate could be isolated. The
microanalytical data and the mass spectrum (molecular ion isotope
signature) show the presence of 2 chlorine atoms in the product.
Titration of the analytical sample shows the presence of one labile
chlorine. The other, inactive chlorine atom has been shown to be

bonded to carbon in the 5 position. Under essentially the same
experimental conditions DNA (from calf thymus - highly polymerized) can
be chlorinated and the product can be passed through Sephadex (G25-coarse)
to remove traces of degradation products. The fractions containing the
modified DNA (approximately same molecular weight as the original DNA)
gave a positive test with tolidine and liberated iodine from potassium

jdodide solution.

Our preliminary work suggests that a study of the chemistry of the
chloramine reaction products of the bases and their nucleoside and
nucleotide derivatives will provide evidence regarding the nature of the

chemical changes which occur in the DNA macromolecule.
IV. Apollo 11 Sample Analysis

Under Grant NAS 9-9439 we have examined the carbon compounds present in
two samples of Apollo 11 for porphyrin-like pigments. Our results
indicated that lunar fines contain “porphyrin-like pigments" as indicated
by fluorescence spectrometry and analytical demetallation. Major
fluorescence excitation at 390 nm was obtained for 600-690 nm emission.
The abundance of porphyrin-like material was estimated to be about

10¢ ug/g. Similar pigments were found in exhaust products from a

lunar descent engine. Although the infall of meteoritic dust to the
lunar surface is appreciable and may be expected to contain considerable
carbon and associated organic compounds including porphyrins, the data
suggest that most, if not all, of the indicated porphyrin aggregate of
the lunar samples was probably introduced during landing of the lunar

module.
V. Analysis of Natural products by Mass Spectrometry

During the past year research has continued on the structural analysis
by mass spectrometry of natural products isolated from plant, animal and
marine sources. A list of publications resulting from this experimentation

follows:

"Mass Spectrometry in Structural and Stereochemical

Problems - CLXXII: The Electron-Impact Prom ted Fragmentation
of 1,2-Cyclohexanediol" by M. Karen Strong and Carl Djerassi.
Org. Mass Spectrometry 2, 631 (1969).

"Application of Ion Cyclotron Resonance to the Structure
Elucidation of the C,H,0t Ion Formed in the Double
McLafferty Rearrangement" by George Eadon, John Diekman,
Carl Djerassi. J. Am. Chem. Soc. 91, 3986 (1969).

"Mass Spectrometry in Structural and Stereochemical
Problems CLXXVI. The Course of the Electron Impact Induced
Fragmentation of Androstane" by L. Tokes and Carl Djerassi.
J. Am. Chem. Soc. 91, 5017 (1969).

"Mass Spectrometry in Structural and Stereochemical Problems -
CLXXVIII. The Electron-Impact Promoted Fragmentation of
1,2-Cyclohexene Oxide" by M. K. Strong, P. Brown, C. Djerassi.
Org. Mass Spectrometry 2, 1201 (1969).

"Mass Spectrometry in Structural and Stereochemical Problems.
CLXXIX. The Electron Impact Induced Rearrangements of
I-Phenylheptenes. Further Evidence for Double Bond Lability"
by A. F. Gerrard and C. Djerassi. J. Am. Chem. Soc. 91,

6808 (1969). ~

"Mass Spectrometry in Structural and Stereochemical Problems.
CLXXXTII. A Study of the Electron Impact Induced Fragmentation
of Aliphatic Aldehydes" by R. J. Liedtke and C. Djerassi

J. Am. Chem. Soc. 91, 6814 (1969).
VI. Dendral

Further work on this related project has concentrated on the
application of Artificial Intelligence to the analysis of specific

classes of organic molecules.

Ref. "Applications of Artificial Intelligence for Chemical
Inference. III. Aliphatic Ethers Diagnosed by Their
Low-Resolution Mass Spectra and Nuclear Magnetic Resonance
Data" by G. Schroll, A. M. Duffield, Carl Djerassi, B. G.
Buchanan, G.L. Sutherland, E. A. Feigenbaum, and
J. Lederberg. J. Am. Chem. Soc. 91, 7440 (1969).
VII. Computer Aided Research Instrumentation

Three principal areas of effort this period were: 1) Continuing use of
and improvements of the ACME time-shared computer for instrumentation,
primarily with the double focus high resolution and quadrupole mass
spectrometer, 2) Support of the current cell separator project described
in the section VIII, and 3) Instrumentation for the Apollo 11 Sample

Analysis described in section IV.

The first two items represent continuing use of the ACME-LINC instrumented
components described in previous status reports. ACME use is now in a
mature state of development. Our experiences with this instrumentation
computer and such continuing work as the mass spectrometers mentioned,

now give us a sound basis for a review of the ACME computer instrumentation
experiment. Prima facie evidence is that it is useful and that it has
demonstrated the feasibility of time-shared computers for laboratory
instrumentation. This experience will enable us to incorporate

improvements into a still more powerful laboratory computer terminal.

The accomplishments to date have been the source of considerable external
interest. The work has been reported in papers given at a number of
technical society conferences on mass spectroscopy, chemistry, and
computers. A rather continuous flow of visitors, representing perhaps

20 to 30 institutions per year, are shown the mass spectrometers and
computer systems. There have been three invited communications in this
last reporting period: One request was for an article to appear in

April 1970, RESEARCH/DEVELOPMENT; a request for a contribution for a
forthcoming text edited by Professor Waller, Oklahoma State, and an

invited paper to the 1970 Pacific Conference on Chemistry and Spectroscopy,

San Francisco.

A commercial version of our GLC-MS computer control interface is produced

by Systems Industries, Sunnyvale, California.
The instrumentation for the Apollo 11 porphyrin analysis using magnetic
circular dichroism (MCD) involved the development of two unique features
of computer instrumentation which are described here. The instrument
itself, a magnetic circular dichrometer, for the purposes of this
description may be assumed to have the signal attributes of a motor
driven scanning spectrophotometer. (Actually it is far more complex

with circular polarized modulating facilities, supercooled magnets, etc.)
The output is detected by a photomultiplier. A commercial phase-locked

amplifier is used for electronic signal detection.

The computer system function for both control and data acquisition. The
wavelength scan drive motor was replaced with a stepping motor to give

the computer digital control of the wavelength to be sampled.

Two unique features were used at the data acquisition interface. First,
the use of a stepping motor permitted a full integrator in the signal
path to improve signal to noise. With the computer control, there was
fast instrument changes in wavelength between observations and a
statistically stationary signal during observations. The integrator
channel has the minimum bandwidth commensurate with the sampling time.
The second feature is designed to optimize the information rate vs
acquisition time. The integration time of the signal integrator is
chosen to be inversely proportional to time. Figure 1 is an abbreviated
schematic. Simultaneously with start of signal integration, a time
signal (generated as a ramp voltage) is started. The increasing signal
at the signal integrator output, (both plus and minus to check for
absolute magnitude) and the time signal are monitored by a comparator.
When any one of these reaches a predetermined value, Vref,» a demand
pulse is generated. At that time the computer reads both the integrated

signal and time signal.

The sample time, T, and instrument dwell is a maximum for small signals
and a minimum for large signals. The computer calculates the signal

value by performing the division S = fsdt/T.

10
TT

Signal Integrator

 

 

 

 

 

 

 

 

 

 

s. signal 1
-
”
Reset
Integrat
Veet NN
}
u
Time ramp
generator

bral

Comparator
When any input

 

 

 

 

 

 

 

 

 

 

 

 

 

 

reaches Vref

  
 

a' Demand Read
Pulse is
generated

~

    

 

 

 

 

 

 

ref
Analog to Digital
S's converter
nn
Sample Multi-
— and plexer
Hold
Reset

 

Figure 1, The schematic of the circuit to acquire the signals fs dt and T. The

computer then calculates S$ = Ss dt/T.

YY

AmMryAcvwveon

 

oF
Figure 2 is a graphical representation showing the locus of sample points.
Note that either, or both, fsdt or T will always be at the most advantageous

portion of the A-to-D range, near full scale.

Js

mo
*Each value of s sampled as two
a
values, s and T

LG s limit

  

 

T
Recorded
Time

Saturation

~10005

 

T limit

  

 

-2000

 

Figure 2. A locus of fs and T for various levels of signal (S).

12
VIII. Cell Separation
A. High Speed Fluorescent Cell Sorter

This unit is designed to measure the fluorescence of cells in a jet

of liquid, break up the jet into uniform drops and divert those drops
containing cells with different fluorescent characteristics into
different containers. During the early part of this period, testing
continued on separation of fractions enriched in plaque forming cells.
The successful results of some of these tests were reported in Sciencel,
The latter part of the period was devoted to constructing a second
improved version of the apparatus, based on the sheath flow system
previously described. The interest generated in the application of the
cell sorting technique to medical problems, particularly to differential
white cell counting, has resulted in the award of a grant from the
National Institutes of General Medical Sciences for further work

(Grant NIH GM 17367).
B. High Speed Volumetric Cell Sorter

This unit measures the volume of cells by determining the change in
electrical resistance in a small orifice containing flowing conducting
liquid as the essentially nonconducting cells pass through. Downstream
of the orifice a jet is formed and deflected in the same fashion as in
the fluorescent cell sorter. The sheath flow system has been applied
to this system and the clogging problems previously experienced with

sufficient concentrations of protective protein have been overcome.

A series of measurements of volume distribution of red blood cells
samples, including some from patients with various sorts of pathological

conditions has been begun. It appears that diagnostically valuable

1 Hulett, H. R., W. A. Bonner, J. Barrett, L. A. Herzenberg. "Cell
Sorting: Automated Separation of Mammalian Cells as a Function of

Intracellular Fluorescence!’ Science 166, 747 (1969).

13
relations between the volume distributions and such conditions as
reticulocytosis (where a large percentage of the cells are immature and

thus larger than normal) can be made with this instrument.
C. Use of Fluorescent Techniques to Test Immunological Compatibility

As mentioned in the last report we have been working on an NIH contract
(NIH 69-2064) to build and test an automated version of the fluorochromatic
histocompatibility test, using the technique developed in the cell

sorter work. An automated system for picking up and delivering micro
samples has been built and is undergoing preliminary testing. In

addition semi-automated experiments have shown that the system should be
approximately an order of magnitude more sensitive than the presently

used manual tests. Such increased sensitivity may be extremely important
in testing for possible immunological rejection problems between

proposed donors and recipients in organ transplants. A description of

this work has been submitted for publication in Transplantation.

14
IX, Optical Data Processing

We have constructed a simple and flexible optical data processing
system with which we have performed experiments directed toward
determining the applicability of such a system to the analysis of

Mariner Mars 1971 Orbiter imagery data.

The system consists of a 1090 milliwatt helium-neon laser, and assorted
lenses, holders, apertures, and shutters, mounted on an optical bench
fabricated from a nineteen foot section of steel H-hbeam. We have
acquainted ourselves with many of the idiosyncracies of coherent light
systems such as sensitivity to film cleanliness and lens imperfections,
and we have developed a general familiarity with operational problems

exclusive of those associated with matched filter applications.

Our prime interest has been to ascertain the extent to which optical
data processing procedures could be called upon to supplement the

real time capability to perform digital computer manipulation of the
data.

For present purposes, the interesting feature of the coherent optical
data processing system is the existence between the input and output
image planes of a transverse plane containing the spatial frequency
Fourier transform of the spatially variable input plane film trans-
mittance. The system therefore lends itself particularly well to image
transformations suited to performance in the Fourier domain.

We have established as our principal finding that if coherent noise
such as that characteristic of the Mariner Mars 1969 Fly-By data,

is present in 1971, it can be suppressed by performing appropriate
masking transformations to the power spectrum in the Fourier plane.

It must be appreciated however, that it is not likely that this
operation nor any other can be carried out with a cleanliness or a
precision matching that of an appropriately programmed digital computer.
If, however, the computer capability is saturated by other demands, a

degree of coherent noise removal can be achieved.

15
It is also possible to undertake a modes degree of restoration of
modulation transfer function image degradation. The results of such
operations are not likely however to significantly enhance the
quantitative merit of the images because of the introduction of
unavoidable image artifacts intrinsic in practical applications of

these techniques.

X. Quasi-Microscope

The proposed Viking Mars 1975 Lander facsimile camera has a spatial
resolution capability of ~ 1 mm. at minimum range. We have investigated
the possibility of introducing a remote auxiliary lens for the purpose
of utilizing the system in a quasi-microscope mode. Remote location
(e.g. 100 or 200 cm range) enables the achievement of microscope
capability without jeopardizing the panoramic function of the system,
such as could result from the malfunction of an auxiliary lens integral

to the camera mechanism.

It has been determined, for example, that the placement of a 49 mm
diameter F/1 lens at a range of 200 cm. will enable acquisition of an
unvignetted image composed of 490 pixels at a spatial resolution of
25 microns. The optics have been studied in some detail and general
system equations have been derived. Depth of field relations have
been established andan incidental wide angle monitoring and quick

scanning capability has been established.

16
XI. Other NASA Mission Activities

During this period Professor Lederberg and Dr. Levinthal have been

directly involved in Mariner Mars 1971 and Viking 1975 mission activities.

Professor Lederberg is a principal investigator on the MM '71 Television
Team and Chairman of the Exobiology Discipline Group of that team. Dr.
Levinthal is co-investigator on the team and a member of the Exobiology
Discipline Group. He has served on the Hardware Task Group and is now
chairman of the Data Processing Task Group and a member of the Mission

Operations Planning Group.

Professor Lederberg has been a consultant to the Biology Instrument
Team and is an investigator on the Biology Science Team for the Viking
'75 mission. Dr. Levinthal served on the Imaging Instrument Team and

is an investigator on the Lander Imaging Science Team.

Dr. Halpern is a co-investigator on one of the Lunar Sample Analysis

Teams.

Drs. Lederberg, Levinthal and Halpern have been supported in these

activities by other members of the Instrumentation Research Laboratory.

17
XII. Environmental Perspective

As part of our practice of investing a modest portion of our effort

into the exploration of new areas of potential mutual interest to NASA

and to our laboratory, two members of our group with a particular interest
and involvement with environmental issues have sought to develop an
environmental overview. As an incentive for the orderly collection of

the material and an outlet for their findings, they are in the process

of presenting a unique type of course in the university system entitled

"Population, Technology, and Environment - A Search for Perspective."

The emphasis in the course is on the presentation of fundamental data
and facts with regard to basic properties and resources of the physical
and biotic global and domestic environment. Human influence upon the
environment is then developed, with particular emphasis being devoted
to immediate insults to the life system, to potentially irreversible
alterations of the environment, and to the exhaustion of non-renewable
resources. The last part of the course will be devoted to a discussion

of remedial actions.

18
XIII, REPORTS , PUBLICATIONS AND PAPERS

July 1, 1969 - Jan. 1, 1970

PUBLICATIONS

1.

10.

G. W. Hodgson, E. Peterson, K. A. Kvenvolden, E. Bunnenberg, B. Halpern,
C. Ponnamperuma, "Search for Porphyrins in Lunar Dust Returned from
Apollo 11," Science 167, 763 (1970).

C. Ponnamperuma, K. Kvenvolden, S. Chang, R. Johnson, G. Pollock,

D. Philpott, I. Kaplan, J. Smith, J. W. Schopf, C. Gehrke, G. Hodgson,
I. A. Breger, B. Halpern, A. Duffield, XK. Krauskopf, E. Barghoorn,

H. Holland, K. Keil, "Search for Organic Compounds in the Lunar Dust
from the Sea of Tranquillity, Science 167, 760 (1970).

B. Halpern, G. W. Hodgson, E. Bunnenberg, E. Peterson, K. Kvenvolden,
C. Ponnamperuma, ‘Search for Organic Matter on the Moon," Geochemica
et Cosmochimica Acta (in press, 1970).

W. Pereira, V. A. Bacon, W. Patton and G. E. Pollock, B. Halpern,
“The Use of Phenylethylisocyanate in the Optical Analysis of
Asymmetric Secondary Alcohols by G.L.C.," Anal. Let. 3, 23 (1970).

I. S. Forrest, L. G Brooks, S. D. Rose, B. Halpern, V. A. Bacon, and

J. Silberg, "Fluorescent Labelling of Psychoactive Drugs,'' Agressologie
(in press, 1970).

W. Pereira, V. Close, W. Patton, and B. Halpern, "Transesterification
with an Anion-Exchange Resin,'' Jour. Org. Chem. 34, 2032 (1969).

W. Pereira, V. A. Close, E. Jellum, W. Patton and B. Halpern,
"Alcoholysis of the Merrifield-Type Peptide-Polymer Bond with an
Anion Exchange Resin," Aust. J. Chem. 22, 1377-49 (1969).

B. Halpern, "Optical Activity” for "Exobiology and the Exploration
of Mars,” Applied Optics 8, 1349 (1969).

B. Halpern, W. Patton and P. Crabbe, "Cotton Effect of Some Derivatives
of Amino Acids and Amino Alcohols," J. Chem. Soc. B, 1143 (1969).

E. Jellum, V. A. Close, W. Patton, W. Pereira, and B. Halpern, "A

Gas-Liquid Chromatographic Method for the Determination of
Phenylalanine in Serum," Anal. Biochem. 31, 227 (1969).

19
11.

12.

13.

14.

15.

16.

17.

is.

V. Bacon, E. Jellum, W. Patton, W. Pereira, and B. Halpern,
"Peptide Sequencing by Low Resolution Mass Spectrometry I. The

Use of Acetylacetonyl Derivatives to Identify N-Terminal Residues,"
Biochem. and Biophys. Res. Comm. 37, No. 6, 1969.

 

E. Jellum, V. A. Bacon, W. Patton, W. Pereira, Jr., and B. Halpern,
"Quantitative Determination of Biologically Important Thiols and
Disulfides by Gas-Liquid Chromatography," Anal. Biochem. 31, 339-347
(1969).

W. Patton, E. Jellum, D. Nitecki, W. Pereira and B. Halpern, "The
Modification of Phenylalanine Containing Cyclo-Peptides with
Nitrosyl Chloride," Aust. J. Chem. 22, 2709 (1969).

D. P. L. Sachs, E. Jellum and B. Halpern, "Determination of the
Stereospecific Hydrolytic Action of Peptsin by Nuclear Magnetic
Resonance Spectroscopy,’ Biochim. Biophys. Acta 198, 88 (1970).

 

S. Liebes, Jr., "Brightness - On the Ray Invariance of B/n2," Am.
Jour. Phys. 37 (9), 932 (1969).

H. R. Hulett, W. A. Bonner, J. Barrett, L. A. Herzenberg, "Cell
Sorting: Automated Separation of Mammalian Cells as a Function of
Intracellular Fluorescence," Science 166, 747 (1969).

5S. Liebes, Jr., "Gravitational Lens Simulator," Am. J. Physics
37, 193 (1969).

H, R. Hulett, L. A. Herzenberg, W. A. Bonner, P. L. Wolf, "Rapid
Cell Sorter - A New Tool for Cell Study with Clinical Applications,"
Laboratory Investigations (in press). To be presented at the 59th
Annual Meeting of the International Academy of Pathology, Mar. 10-14,
1970, St. Louis, Mo. °

20