Abstract: | The adenylate cyclase activity of human ejaculated spermatozoa in broken-cell preparations was investigated. In the presence of 5 mM metal cations and 0.1 mM ATP, the relative enzyme activity with Mn2+, Ca2+, Mg2+, Ba2+ was 1.00, 0.28, 0.22, and 0.03, respectively. Added Ca2+ appeared to activate the enzyme in the presence of Mn2+ or Mg2+. The human sperm adenylate cyclase was stimulated by ~ 2-fold by free Ca2+ (lmM) in the presence of Mg2+ (5 mM). If the GTP analogue, 5′-guanylyl imidophosphate (Gpp(NH)p) was added to the sperm homogenate in the presence of 200 μM ethylene-glycol-bis (β-aminoethylether) N,N′-tetraacetic acid (EGTA), the adenylate cyclase activity was increased by approximately 25%, but with the addition of 280 μM Ca2+ there was a decrease in enzyme activity. A similar response to low concentrations of Ca2+ was obtained after complementation of the sperm enzyme with the guanine nucleotide regulatory component from human erythrocytes, where the addition of 40 μM Gpp(NH)p, 200 μM EGTA, and Ca2+ (≤ 160 μM) stimulated the sperm enzyme ~ 3–4-fold, but the further addition of Ca2+ (280 μM, final) neutralized the stimulatory effect. The addition of adenosine, and the nucleotides 5′-AMP and 5′-ADP inhibited the enzyme, whereas guanine and 5′-GMP had no appreciable effect. Human follicular fluid and serum also had little direct effect on the sperm adenylate cyclase. These resuls suggest that Ca2+ might be an important physiological modulator of the human sperm adenylate cyclase. |