Acetylation Studies

Abstract

In an earlier paper 1 experiments were recorded as evidence for the belief that acetylation studies might prove of value in elucidating phases of intermediary metabolism. In this communication we record further experiments dealing with acetylation.

p-Aminobenzoic acid is partially acetylated by the rabbit forming p-acetyl-aminobenzoic acid, a substance which can be recovered from the urine. (Qualitative tests make it quite evident that some of the p-aminobenzoic acid is also eliminated in the form of its glycuronate salt; but this will be the subject of another communication.) Since carbohydrates—and possibly fats—are probably the source of the acetyl group furnished for the acetylation process, it became of interest to determine the effect of the injection of insulin upon the amount of acetylated product produced.

The results show that the injection of 0.5 units of insulin per kilo wt. raised the normal acetylation value of 20-25% to that of 44-47% of the original p-aminobenzoic acid injected. Although the rabbits showed individual variations in their ability to acetylate, insulin, in each case, practically doubled the output of the acetylated product.

We next determined what effect the simultaneous injection of insulin and reduced glutathione would have upon the output of the acetylated product. The belief is prevalent that the -SH group has an inhibiting action in so far as insulin activity is concerned. For example, Du Vigneaud 2 has shown that insulin can be inactivated if it is mixed with cysteine or reduced glutathione in a neutral solution in an atmosphere of nitrogen, because the blood-sugar of the rabbit does not drop when the insulin-glutathione (or insulin-cysteine) solution is injected. Instead of mixing our reduced glutathione and insulin in vitro, we decided to inject them separately, but simultaneously. Five mg. of reduced glutathione and 0.5 units of insulin (per kilo of body weight) were injected.