Purification, characterization and possible function of α-N-acylamino acid hydrolase from bovine liver

Abstract

α-N-Acylamino acid hydrolase from bovine liver has been purified approx. 1700-fold with a yield of 28%. Based on the results of studies using polyacrylamide gel electrophoresis the purified enzyme is homogeneous. This enzyme catalyzes the hydrolysis of α-N-acylated amino acids to yield the acyl group and the corresponding amino acid, α-Acetylmethionine was the most rapidly hydrolyzed substrate tested for this enzyme. Most of the other α-N-acylated amino acids used as substrates were hydrolyzed. Some, however, were cleaved at less than 1% of the rate observed for N-acetylmethionine, α-N-Acylamino acid hydrolase did not catalyze the hydrolysis of $\text{N-}\text{acetyl-}\text{d}\text{-alanine}$, N-acetyl-β-alanine, ϵ-N-acetyllysine, N-acetylglycinamide or α-N-acetylated peptides. When incubated with this enzyme the chloroacetyl derivatives of leucine and valine were hydrolyzed approx. 8- and 3-times, respectively, more rapidly than the corresponding N-acetyl derivatives. On the other hand, N-formylmethionine was hydrolyzed at only 60% the rate of N-acetylmethionine. Other studies on α-N-acylamino acid hydrolase have shown that it is a dimer composed of two 40 000 molecular weight monomers, it is active over a broad pH range with maximal activity at approx. pH 8.5, and requires Zn²⁺ for enzymatic activity. The substrate specificity and other properties of bovine liver α-N-acylamino acid hydrolase are very similar to those reported for acylase I isolated from porcine kidney [7]. We suggest that this enzyme functions in the catabolism of α-N-acetylamino acids resulting from the turnover of α-N-acetylated proteins.