Untersuchung zur Chemie der Arterien wand, X. Über die saure Carboxypeptidase in der Aorta des Rindes

Abstract

A carboxypeptidase, which can be demonstrated in bovine arterial wall, was purified 225-fold by ammonium sulfate precipitation and gel filtration. This arterial enzyme differs from the known carboxypeptidase in the following properties: the optimum pH is 4.6, and the optimum temperature is 47[degree] during a 2 hr incubation period. Synthetic substrates of arterial carboxypeptidase are tripeptides and, to a lesser extent, tetrapeptides with a branched, aliphatic (leucine, valine) or aromatic (phenylalanine) amino acid at the C-terminal end; of these, the highest rates of hydrolysis are shown by peptides with C-terminal leucine. Substrates with pre-terminal leucine are more easily hydrolyzed; pre-terminal histidine prevents hydrolysis, and C-terminal glycine is not removed by by hydrolysis. The Michaelis constants of the tripeptides Ser-Leu-Leu, Leu-Leu-Leu, Leu-Leu-Val and Gly-Gly-Phe are 0.28, 1.06, 2.7 and 1.37 (mM). The enzyme does not attack the synthetic substrates of pancreatic carboxypeptidase A and B, the catheptic carboxypeptidases or ca-thepsins A, B and C. It possesses no esterase activity. The activity of arterial carboxypeptidase is neither altered by the addition of metal ions, nor inhibited by sulfhydryl reagents (p-chloromercuribenzoate, iodoacetate, N-ethyl-maleimide). Arterial carboxypeptidase does not attack bovine serum albumin, the B-chain insulin or chondroitin sulfate-protein but it acts upon their proteolytic cleavage products to give free leucine, valine, phenylalanine and tyrosine. On the basis of the low optimum pH and the relative specificity, the enzyme should be designated: acidic (leucyl-)carboxypeptidase (peptidyl-leucine-hydrolase).