Cyclic AMP Induced Incorporation of 33Pi into Human Spermatozoa Membrane Components

Abstract
Three protein components of human spermatozoa membranes served as substrates for protein kinases. Protein III (.apprx. 50,000 MW) was phosphorylated only under stimulation by exogenous cyclic[c]-AMP, while protein II (.apprx. 80,000 MW) phosphorylation was independent of the presence of the cyclic nucleotide. Protein I (.apprx. 105,000 MW) that accounts for an important percentage of the total spermatozoa membrane protein, showed the highest phosphorylation rate under cAMP stimulation. The cAMP mediated alterations in the structural and biochemical properties of the human spermatozoa are apparently produced through phosphorylation of specific membrane proteins. It may also be suggested that modifications of the tertiary and quaternary structure of the plasma membrane proteins, through cAMP stimulated phosphorylation, may be requirements for the initial steps of capacitation.