Porcine Liver Succinyltrialanine p-Nitroanilide Hydrolytic Enzyme. Its Purification and Characterization as a Post-Proline Cleaving Enzyme

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Abstract
Succinyltrialanine p-nitroanilide(STANA)-hydrolytic enzyme was purified 5,200-fold from porcine liver soluble fraction with a yield of 75% by ammonium sulfate fractionation and chromatographies on DEAE-Sephacel, Sephadex G-150, and hydroxylapatite columns. The purified enzyme was homogeneous as judged by polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate (SDS). The pI of the enzyme was 4.9 by disc gel electrofocusing and the molecular weight was calculated to be 72,000 by gel filtration on a Sephadex G-150 column and 74,000 by SDS-polyacrylamide gel electrophoresis. Acidic amino acids amounted to 17.2% of the total amino acid residues, and the basic ones, 12.9%. No hexosamine was detected. The STANA-hydrolytic enzyme showed maximal activity at pH 7.4 against succinyltrialanine p-nitroanilide and at pH 6.5 against succinyl-Gly-Pro-4-methylcoumaryl 7-amide (MCA), and was stable between pH 6 and 7 in the presence of dithiothreitol. This enzyme hydrolyzed succinyl-Gly-Pro-Leu-Gly-Pro-MCA, succiny-Gly-Pro-MCA, succinyl-Ala-Pro-Ala-MCA, and several proline-containing natural peptides in addition to succinyltrialanine p-nitroanilide, but was unable to hydrolyze the substrates of aminopeptidases, dipeptidylamino peptidase IV, trypsin, and chymotrypsin. Elastatinal and chymostatin were effective inhibitors and their IC50 values were 8.7 μg/ml and 18.2 μg/ml, respectively. The enzyme was completely inhibited by 10−7 M p-chloromercuribenzoic acid (pCMB), 10−7 M p-chloromercuriphenylsulfonic acid (pCMPS), and 10−4 M diisopropyl phosphofluoridate (DFP), but not by 1 mM E-64, which is known as an inhibitor specific to thiol proteinase. The enzyme was easily inactivated by agitation in a Vortex mixer, and its activity was recovered by the addition of thiol compounds such as dithiothreitol, 2-mercaptoethanol and cysteine. The effects of inhibitors and thiol compounds were substantially identical when the enzyme activity was measured with either succinyltrialanine p-nitroanilide or succinyl-Gly-Pro-MCA as a substrate. These results indicate that the STANA-hydrolytic enzyme in the liver soluble fraction is a post-proline cleaving enzyme [EC 3.4.21.26].

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