On the utilization of L- and D-alanine for the acetylation reaction in vivo.

Bloch and Rittenberg (1, 2) have reported that deuterio-nn-alanine and acetylamino acids labeled with deuterium in the acetyl group give rise to a large isotope concentration in the acetyl groups of amines containing an a-hydrogen atom, in contrast to amines not having an a-hydrogen atom. With deuterioacetic acid itself, no such difference in the acetylation of the two types of foreign amines was found, while deuteriopyruvic acid gave qualitatively similar though lower values than nn-alanine. Bloch and Rittenberg suggested that pyruvic acid, arising by deamination of alanine, could condense directly with phenylaminobutyric acid by the mechanism proposed by Knoop (3) and others (4) and that acetylation of p-aminobenzoic acid, on the other hand, took place only after conversion of the labeled pyruvic acid to acetic acid. In a previous communication (5), differential acetylation of the two types of amines with carbon-labeled pyruvic acid was observed in a laboratory strain of rats of unknown origin.’ In the Sprague-Dawley strain, on the other hand, it was found that the acetyl groups of the two types of amines had identical isotope concentrations after administration of carbon-labeled pyruvic acid (5). This has now been found to be the case also with three additional strains of rats (Table I). The ability of carbon-labeled m-lactic acid to serve as a precursor for the acetyl groups of the two kinds of amines has also been tested and compared to that of pyruvic and acetic acids. The resulting isotope concentrations (Table II) are identical in both types of acetylamines. Since the data obtained with carbon-labeled pyruvic and lactic acids were in disagreement with the results of Bloch and Rittenberg with deuterio-m-alanine, acetylation experiments with carbonand deuterium-labeled Land n-alanine were carried out.