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 (approx. 50,000 M W) was phosphorylated only under stimulation by exogenous cyclic-AMP, while protein II (approx. 80,000 M W) phosphorylation was independent of the presence of the cyclic nucleotide. Protein I (approx. 105,000 M W) that accounts for an important percentage of the total spermatozoa membrane protein, showed the highest phosphorylation rate under cyclic-AMP stimulation. These observations suggest that the cyclic-AMP mediated alterations in the structural and biochemical properties of the human spermatozoa are 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 cyclic-AMP stimulated phosphorylation, may be requirements for the initial steps of capacitation.