Dr. Sol Splegelman,
Dept. Bacteriology,
University of Diinois,
Urbana, Dlinois.

Dear Sol:

Enclosed herewith is about 50 mg. of o-nitrophenyl-b-D-galactopyranoside
which should suffice for a considerable number of galactosidase determinations.
I have been using it at 4/2000 (.15 mg/ml), developing the color either at
pH 7.5 in the buffered reaction mixture, or by adding Na,00, to W/10 after the
reaction is completed. M/50,000 nitrophenol has an optical density of 0.1 in
an 18. mm. testtube at 4200 K » 80 that you can easily work in a range of
negligible change in substrate concentration. If K, is not too high, you aould
probably even use the substrate as low as 107” M or lower.
| I will have some detailed directions on the synthesis for you ina couple
of days. It involves the preparation of aceto~brom-galactose, and coupling it
with o-nltrophenol in alkaline solution. Ths nitrophenyl-galactoside pentacetate
ia then hydrolysed with Ba(OH) 2 in alwahol. The prep. is supposed to be quite
smooth, givgfing readily crystallised products in high yield.

Sincerely,

Joshua Lederberg