On the acetylation of aliphatic amines by kidney preparations.

The feeding of p-aminobenzoic or cr-amino-y-phenylbutyric acid to rats results in the excretion of acetylaminobenzoic or acetylphenylaminobutyric acid in the urine. Simultaneous feeding of isotopically labeled compounds such as acetic or pyruvic acid (1, 2), Dor L-alanine (3), Dor L-serine (4), or an acetylaminol acid (5) gives rise to labeled acetyl groups. Whereas most combinations of acetyl precursors and amines give nearly identical results, the isotope concentration of acetylphenylaminobutyric acid is much higher if labeled n-alanine, n-serine, or acetylglycine is fed. To explain these findings, it was suggested (3) that acetylation of phenylaminobutyric acid occurs in part in the kidney (6), and it was further assumed that n-alanine and acetylglycine are converted to acetate in the kidney with little dilution. In contrast, other acetyl precursors are predominantly metabolized in the liver where the metabolic pool of acetate is large (1). p-Aminobenzoic acid (7) is acetylated only in the liver. The in vitro studies reported here support this hypothesis and indicate that acetylation in the kidney may be due to a reversal of hydrolysis catalyzed by the enzyme acylase (S), in contrast to a transfer reaction which appears to be the mechanism of acetylation in the liver (9).