Physicochemical and kinetic properties of the Mn2+-dependent adenylyl cyclase of the human testis.

Abstract

The present study shows the presence of a soluble Mn2+-dependent adenylyl cyclase (AC) in the human testis and some physicochemical and kinetic properties have been examined. The results can be summarized as follows: 1) At 35 C the AC activity was constant as a function of incubation time for at least 60 min and proportional to protein concentration ranging from 10–150 jug protein per assay tube. 2) Enzyme activity was maintained for at least 24 h at 4 C; at 35 C, however, a marked loss of activity (approximately 40%) was observed after 2 h. At higher temperatures (above 45 C) the activity was destroyed completely after a few minutes. 3) The AC exhibited a pHoptimum around pH 7.5 and increasing ionic strength (0–0.4 M NaCl/KCl) apparently had no significant effect on enzyme activity. 4) Free cysteinyl thiol groups are required for enzyme activity: alkylating agents (N-ethylmaleimide, 0.8–6.0 mM) and reducing agents (β-mercaptoethanol, 1–5 mM) enhanced AC activity. 5) The Mn2+-dependent AC activity was ins...