The hydrolysis of dipeptides and aminoacyl naphthylamides by the human seminal plasma.

Abstract

Summary. High dipeptidase and aminopeptidase activity is present in human seminal plasma. The two activities can be easily and clearly separated from each other by chromatographic procedures. Each of the three dipeptidase fractions has characteristic substrate specificity but is not affected by divalent metals. The seminal aminopeptidase activity is inhibited by EDTA and activated by cobalt. Among the enzymic constituents of the human seminal plasma is a number of proteases (Mann, 1964). Some of them have been partially purified and charac¬ terized by Lundquist (1953), who described an aminopeptidase, which readily hydrolyses both di- and tripeptides to leucylpeptides, without any preference. During recent years, however, several new chromogenic substrates have been introduced to the study of proteolytic activity (Nachlas, Goldstein & Seligman, 1962), and the seminal aminopeptidase has been shown to hydrolyse some of the newly synthesized aminoacyl naphthylamides (Krampitz & Doepfmer, 1961), as well. In the course of a study on the seminal proteases, we have been able to demonstrate that, contrary to the previous reports, the dipeptidase and aminopeptidase activities are well separated in the human seminal plasma. Pooled semen from an infertility laboratory was used. It was fractionated by DEAE-cellulose chromatography or Sephadex G-100 gel filtration. Semen samples were diluted with equal volumes of the elution buffer (20 mMtris-HCl buffer, pH 7-6). Aminopeptidase activity was estimated using a num¬ ber of 1 -amino acid naphthylamides as substrates and determining the amount of naphthylamine liberated with/>-dimethyl-aminobenzaldehyde. The hydroly¬ sis of the dipeptides was followed with a pH-stat (Jacobsen, Leonis, Linde¬ strom-Lang & Otteson, 1957). In DEAE-chromatography, the aminopeptidase activity was clearly separate from the dipeptidase activity (Text-fig. 1). The latter was present in three different Chromatographie fractions which could also be obtained by filtration of seminal plasma through a Sephadex G-100 column. The hydrolysis rate of various dipeptides (gly-gly, gly-leu, gly-phe ala, ala-gly, pro-gly) by the fractions varied considerably (Text-fig. 2), but neither EDTA nor any of the