Membrane-Bound Adenylate Cyclase Activity in the Testis of the Blue Fox

Abstract

Membrane-bound adenylate cyclase (AC) activity was much higher in the presence of Mn²⁺ than of Mg²⁺. The Mn²⁺ -sensitive adenylate cyclase (MnAC) showed a linear rate of activity for at least 60 min. In contrast, the Mg²⁺ -sensitive AC (MgAC) displayed a considerable burst in activity, so that after 90 min of activity it was approximately tenfold higher than at the start of incubation. Guanine nucleotides enhanced MgAC activity; 10⁻⁶ to 10⁻⁵ M of 5′-guanylylimidodiphosphate caused a threefold stimulation. The MgAC could be stimulated by hormones (FSH, hCG, PGE₁, isoproterenol, glucagon), the highest activation being achieved with FSH. Increasing levels of ATP produced a concentration-dependent increase in MgAC activity. The apparent affinity of the AC for MgATP increased threefold (K_m 0.50-0.15 mM) by raising the free Mg²⁺ concentration from 0.4 to 10.0 mM. The membrane-bound AC of the blue fox testis is thus regulated by hormones, Mg²⁺, and guanine nucleotides in a similar manner to ACs in other somatic cells and in testes from other species. The high MnAC activity in membrane particles from these testes probably represents membrane-bound AC activity in germ cells. The burst in MgAC activity during incubation may represent proteolytic activation of membrane-bound germ cell AC, with a gradual appearance of Mg²⁺ sensitivity.

Key Words:

• Testis
• Adenylate cyclase
• Membrane particles