Letter from Melvin Cohn, Washington University School of Medicine to Michael Heidelberger
Biochemists and other biomedical researchers depend on one another for substances and preparations they used in their experiments.
Cohn here mentioned that he was supplying Heidelberger with B-galactosidase, an enzyme that helps bacteria ferment sugar and
that played a key role in bacterial genetics research in the 1950s. Cohn also mentioned the use of radioactive tags to identify
individual proteins in solutions.
Number of Image Pages:
1 (70,174 Bytes)
1956-11-20 (November 20, 1956)
Washington University School of Medicine
Reproduced with permission of Melvin Cohn.
Medical Subject Headings (MeSH):
Antigens and Antibodies: Heidelberger and The Rise of Quantitative Immunochemistry, 1928-1954
Since our exchange of letters I have spent some time in between teaching sessions preparing and purifying some Beta-galactosidase
for you. I am sending today 25 ml. of a preparation which contains 1.1 x l0^6 units per ml. This preparation is about 70
per cent pure. One unit of enzyme is 1 mM of o-nitrophenol- Beta-D-galactoside hydrolyzed per minute at 28 degrees C, pH 7.0,
M/1O sodium phosphate buffer. This enzyme is sodium activated and we therefore work in all sodium buffer.
Since you will be trying to find either enzyme precipitation or enzyme inhibition by your anti-galactose sera, I am including
some of the o-nitro-phenol-Beta-galactoside substrate. We generally run our assays using M/500 O-nitro-phenol-Beta-galactoside
under the above conditions. In the Beckman 1 mole of o-nitrophenol liberated equals an optical density of 1.0 at 420 mole.
One other note of caution: This enzyme which I am sending you is a by-product of another experiment which I carried out about
4 months ago. The solution I am sending you is radioactive. The enzyme is unlabeled but the contaminating proteins are labeled,
and therefore you would want to be reasonably careful so as not to contaminate your lab. The radioactivity is sufficiently
low not to be a health hazard, only a contamination hazard.
Once again, I am sorry about my delay in sending this and I hope that something exciting comes out.