Aminopeptidase A in reproductive organs of the male rat: evidence for high activity in the posterior lobe of the prostate.

Of the reproductive organs of the male rat a high level of hydrolysis of alpha-L-glutamyl-beta-napthylamide (GluNA) and alpha-L-aspartyl-beta-naphthylamide (AspNA) in the presence of Ca2+ (5mM) (aminopeptidase A) was found in the posterior lobe of the prostate. Histochemically, this enzyme was localized in the epithelial cells of acini, which were grouped in the dorsal part and sharply separated from non-active acini in the anterior part of the lobe. A single peak of Ca2+-activated GluNA and AspNA hydrolysis was obtained after chromatofocusing at pI 4.9 and on anion exchange chromatography this activity eluted at 0.09 M NaCl. After gel filtration on Sepharose 6B a major peak of activity was found at the elution volume (Ve/Vo = 2.28). In all of these fractionation procedures aminopeptidase A was partially or totally overlapped by other aminopeptidases hydrolysing various amino acid-beta-naphthylamides. A pooled enzyme preparation gave an optimum at pH 7.3. The hydrolysis of GluNA was markedly enhanced in the presence of Ba2+, Ca2+ and Sr2+, but the hydrolysis of AspNA was activated only by Ca2+ and Sr2+. Castration caused a significant decrease in the hydrolysis of GluNA by the posterior lobe, but did not influence the low levels of activity in other parts of the prostate or in the seminal vesicles.