Porcine liver aminopeptidase B. Substrate specificity and inhibition by amino acids.:Substrate Specificity and Inhibition by Amino Acids

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Porcine liver aminopeptidase B [EC 3. 4. 11. 6] is highly specific for hydrolysis of β-naphthyl-amides of basic L-amino acids; the Km values for L-arginine β-naphthylamide and L-lysine β-naphthylamide were 0.035 and 0.12mM, respectively. The enzyme was inhibited by various α-amino acids. Among basic amino acids, L-homoarginine and L-arginine were the most potent inhibitors, L-lysine and L-norarginine (α-amino-γ-guanidinobutyric acid) being less inhibitory. Hydrophobic amino acids also inhibited the enzyme competitively. This suggests that there is a hydrophobic region that binds the side chain of the substrates or inhibitors in the specificity site of the enzyme. Studies on the inhibitions by L-arginine derivatives showed that blocking of the α-carboxyl or the α-amino group reduced the inhibitory effect of L-arginine. Porcine liver aminopeptidase B was not inhibited by puromycin, whereas bestatin inhibited the enzyme competitively with a K1 value of 1.4×10-8M. This enzyme had no kinin-converting activity.

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