January 10, 1948.

ore de Sonal,
Inatitut Pasteur,
Faris.
eur Juojes.

I have been waiting te ses your aanuscript before replying, but
evidently it has been delayed. |

I did some work on drug resistance in Kel? a couple of years ago,
urd as I recall did mance to gelect for recombinants using azide and
strentonyein, but this work was not pushed very fer, and i dco not hove
those stocks. Using matritionsl selection, it wes aacy to show that these
resistunce factors segregated and wiles reconbined in cvotetrophe. 1 |
wag unzble then to get any very cleacut proflevine resistant mtsats. If
you would see any advantoce in the attempt , I would be glacito try to
see whather T could succeed in crossing the strains with which you are
having difficulty.
| There is very little more I can add to zene enzyme studies thet f have
hot ublreecy eitten. T balfeve thet I have already tol: you of .ay kinetic
studies of the Ma effect on Kel2 lactase. Je are in process of extracting |
the enzyme, like yourself, from a variety of mtents.

Cne noint worth mentioning, au passant, is that one mutant class (Lac, -7
which has hitherto appeared. to be rigidly Laotoae~negative, is canable of
edapting to produse a galactosiduse whieh will attack lactase, but only
fn the presence of buty) galuctoside, not with lactose. This is a further
indication, that the genetic effects are mostly on the adaptation mechcnisna,
and, for thea most part, do not have to do directly with the specificities
of the enzyies. A further indicution of this is given by the temperature
matent referred to in the enslosed abstract. mekek In this mtant, the effect
of temperature is not on the activity of the enzyme but on its formation.
Before we were aware of your findings on amylomeltase, Doudoroff and I
had been working on the mechanisn of maltose uthiization in the sunoressor
suabdnation Lie3-S.% which is Mal-Gluf. Your findings have teen confirmed,
aad waltose is assLailzted via. volysaccharide both in the suppressor stock
and dn kel2. however, we cannot account for the total utLlization of multose
y3tes in substuntaully
by dry cell prens. contadning

a

awyloualtase, but does not with Iintuct celis, although slucose sunplied |

by intuct cells of the sugressor. Glucose aceu:

  
 

ayuincluy sroportions whan maltose 4s
t L i

to these celis is not tevched. Our ouner has bean submitted to the Jour,
Sioi. Chea., but orobably will not be in print for soue tine.

Until recently, Io had been extracting lnctese in Grean's ‘et crushhage
gill, but at Poudoroff'y suggestion I have now nerely been dvying the calls
at room tecporatare over 25° Luctese is yerr readily extrected with dilute
buffer from the dried cells, This m=*thod his the erest advantsce of ereut
flexibility, «nd is very efficient.

He were doing sons experiments Lately jon getting antibodies to
lactuse, but with no encovragerent 30 far. |

vith bes$ revards,

Cordially,

Joshua Lederberg

tg