April 24, 1950.

Dear Dr. tulofr :       -

  For YV* tim, f havs beten fohi~vdng with groat intorest the vpork of
parssif and your oohleqme m the metabolism of oarbohydratss by micro-
organicma. As I am r&her doubtful that I hme been able to notiae all of
this wark as it has been publiehed, Z beg your favor In pl#&.ng q name
on the maU.ng lfet of your Imtituto, for reprinti of publio~tiom daating
with tiis arubjeet.

Tou IU~JT bs Lrbrrstsd in a ad.1 exptdwmti ik;c that qy be tieful to
tar.. f*urther investigations you my be contemplating on lactase or galaotiridasre.
I have baen studying thfs enzyme In E. ooli, but have abandoned the um of
lactose as substrate, as giving results much too imprmiee. Instead, the corn-
pami 2 - o-titrophenyl-D-galac toside, , qrspsred by coupling nltrophenol with
acetobrc~~g~lactose~ serves aa a very delicate sub&sate fcr amay. The gala&o-
side is essentzMly colorLam, but ia split by gs.l.actcsidasa to yield o-titrophenol,
which is mxmured in alkaltie sl;lution at 4200 8.. fn 9 spactrophotmter or
colorimter. I a.~ prepar5ng a ,mmecript deaoribtng the method, but mention
2t JA case you cm cmteqbtfng further 5tuBlss on tJk13.s emym in tie near
future;.

Yours almerely,

    Joshua Lederberg
Aesietant Profaesor of Gene tiae