A peptidase hydrolyzing DNP-Pro-Gln-Gly-Ile-Ala-Gly-Gln-D-Arg-OH (Peptide III), which was originally designed as synthetic substrate for vertebrate collagenase, was detected in human serum and its enzymatic properties were partially characterized.
1) Assay of the enzyme activity in sera from healthy adults and patients with various diseases revealed that the level of the enzyme in serum was enhanced with hepatic diseases, especially alcoholic and drug-induced hepatitis.
2) In hepatic diseases, Peptide III-hydrolyzing activity was highly correlated with Suc-(Ala)3-pNA-hydrolyzing activity and both enzyme activities were only correlated with γ-GTP among laboratory findings of the patients examined.
3) In healthy adults, both Peptide III-and Suc-(Ala)3-pNA-hydrolyzing activities were higher in male than in female and gradually increased with age. These enzyme activities were correlated with each other (r=0.696, n=78) and with γ-GTP (r=0.688, n=56).
4) Analysis of the molecular size of Peptide III-hydrolyzing peptidase by Sepharose 4B chromatography has shown that, in healthy adults, the break through fraction (MW: about 2,000K) and a fraction corresponding to molecular weight of about 200K contained enzyme activity. In the latter fraction, Suc-(Ala)3-pNA, hydrolyzing peptidase and γ-GTP were coeluted.
5) In serum from a patient with carcinoma recti, however, the third peak showing a high Peptide III-hydrolyzing activity appeared around 800K fraction (coeluted with α2-macroglobulin) where the presence of two enzymes complexed with α2-macroglobulin [against Peptide III and Suc-(Ala)3-pNA] was confirmed. They showed proteolytic activity against gelatin and casein after dissociation from α2-macroglobulin.
6) All the peptidases found in these fractions were metallo-enzymes except a Suc-(Ala)3-pNA-hydrolyzing enzyme complexed with α2-macroglobulin which is inhibited by phenylmetnylsulfonvl fluoride.
7) The origin of serum peptidases against Peptide III and Suc-(Ala)3-pNA was suggested to be a liver microsomal fraction, based on the analysis of subcenular distribution and properties of peptidases in the guinea pig liver.
