NEL Cot — KTS

Maro} 22, 1952.
Dear Cohn

Thank you for your prompt and informative letter. It will take some time
to assimilate fully, but in any case, I can respond with very little mre
than was included in my first letterp and in ay earlier correspondence with
Jacques~ perhaps he might dig this out for you as an equivalent in volume,
if not in quality, to your summary. Your suggestion to exchange mass. bearing
on problems of mitual interest 45 a gcod ons. In compliance, I must admit to
& general paper presented at the Genetics “ociety last Fall, and to be in-
cluded in "Genetics in the 20th Century", to be published soon by MacMillan.
Unfortunately, Stanier now has my only copy, but there is nothing new in it
except 4 surprising convergence of attitudes.

One specific detail in your letter provokes some cusment: the non-utilize-
tion of homomorphous arabinosides by p-D-galactosidass. Mr, Snyder, in Link's
lab just recently prepared sone ound trophenyl—s—R-arabepyrancside to test just
this point. My enzyme prep. from K-12 has sn appreciable activity on this
compound: Vig, about 1:6 compared to ONPG, K, about €/250, so that heavy con-

Centrations must be used to satugnte the enzye (in m/50 Na-Phosphate buffer, 7.5).
There are any number of possible reasons for this Glecrepaasy, but the easiest

way to clear it up would be for you test OHPA yourself. Unfortunetaly our

supply is (as uaual) very limited, and the enclosed sample is a aubstantial

part of thet available now; however, it sould more than suffice for the im
mediate purpose.

Your remarks on ths thlogalactogidez are extremely provocative: {2 you
could perchance spare a reasouably suali quantity of any actively dahibitory
one, I would appreciate the favor, I might add that I had reached the same
concjusion about the sepeability of enzyme—combnation and inductivity from
the behavior of the Lac; amitent: this responds to N-Butyl gal. but not to

lactose; however, the lactase cnee formed acts quite as usual on lactose.

By the way, I hear that Ryan fs isolating mtants "Induced" with galoctceides.
irs. Lederberg and I found several years ago thet Lac~ mitante repeat adly
cropped up in butyl~galactcside broth, but assumed this was due to adverse
selection of high internal BuGH in Lac+ ceils. Id there evidence to rule

out selection?

Rober&@ and his group of blophysicists at Carnegie Terrestrial Magnetiom
(“ashington) were delving pretty deeply into lactase adaptation, but had to
quit for war work. They had some interesting material on adaptation in EF, coli B-
which gces faster in washed suspensions than with most strains.

Sincerely,

- Joshua Lederberg