Activation of Sperm Adenylate Cyclase by Factors Associated with Eggs1

Abstract

The addition of egg factors from Strongylocentrotus purpuratus sea urchins to sea urchin broken sperm cell preparations either had no effect or inhibited the sperm adenylate cyclase. However, when sperm were preincubated with the egg factors prior to cell disruption, the adenylate cyclase was activated by as much as 50-fold. The enzyme activation was due to an increase in the apparent maximal velocity and not to a change in the apparent Michaelis constant for MnATP. Near maximal activation of the sperm adenylate cyclase activity was observed within 1 min after preincubation of egg factors with the intact sperm; this response was observed whether the preincubation was at 0–2°C or at 15°C. Enzyme activation by the egg factors required the presence of Ca²⁺ in the preincubation mixture, with half maximal enzyme activation occurring at Ca²⁺ concentrations between 3 and 5 mM. Concentration response curves demonstrated that equal concentrations of the egg factors caused both a cyclic AMP elevation and an adenylate cyclase stimulation in intact sperm. The adenylate cyclase activator migrated at the void column of various gel columns and had an apparent molecular weight in excess of 5 × 10⁶. These data are the first to describe marked activations of either a vertebrate or invertebrate sperm adenylate cyclase and show that both an intact cell and Ca²⁺ are required in order to observe the activation.