Acetyl Group Determinations in Horse Liver Alcohol Dehydrogenase and in Horse Myoglobin.

Abstract

The main fraction of horse liver alcohol dehydrogenase was subjected to acid hydrolysis followed by an enzymatic microdetermination of acetic acid. Extensive dialysis of the pure protein was necessary in order to remove supposedly adsorbed acetate. When this background was removed the value for acetic acid corresponded to about 2 acetyl groups per molecule of protein. Although this method does not give any indication of where these acetyl groups are situated, the failure to demonstrate an N-terminal amino acid strongly suggests that they represent N-terminal groups. Three fractions of horse skeletal muscle myoglobin were also analyzed. In the hydrolysates of 2 of these it was possible to bring the acetic acid content to nearly zero by extensive dialysis of the pure fractions. In 1 fraction, however, the acetic acid content could not be lowered to less than 0.5[long dash]0.7 moles per mole of protein. This seems to indicate acetate adsorption. That explanation is favored by other considerations as well as by a hydrazino-lysis. It is clearly shown that differences in acetylation status cannot be the explanation for all 3 myoglobin variants.