Regulation of protein phosphorylation and motility of sperm by cyclic adenosine monophosphate and calcium.
Motility and protein phosphorylation have been measured under identical experimental conditions in ejaculated dog sperm lysed with low concentrations of Triton X-100 and reactivated with [gamma-32P]ATP. Cyclic AMP stimulates motility and protein phosphorylation while calcium inhibits motility and the overall incorporation of phosphate into endogenous proteins. Analysis of 32P-labeled sperm proteins on 1- and 2-dimensional polyacrylamide gels demonstrates that an enhanced phosphorylation of a defined number of specific proteins is associated with cAMP-stimulated motility. A major axonemal proteins, namely tubulin, has been tentatively identified as a phosphoprotein subject to regulation by cAMP. The phosphorylation of tubulin is almost completely dependent upon cAMP and is not affected by microM calcium. On the other hand, the cAMP-dependent stimulated phosphorylation of the other sperm proteins still occurs, but in most instances at a reduced rate in the presence of calcium. Two high molecular weight (Mr) phosphoproteins (350,000 and 260,000 daltons) whose phosphorylation states are modified by cAMP and calcium also were identified. It is suggested that 1 or both these proteins may be high Mr subunits of dynein. The phosphorylation of 1 of these proteins is stimulated by cAMP, but not affected by calcium; the other is stimulated by cAMP and inhibited by calcium. Three major cAMP-independent phosphoproteins of Mr 98,000, 43,000 and 26,000 have been identified. The phosphorylation of the 98,000 Mr protein is markedly reduced by micromolar calcium and not restored by cAMP. Using anticalmodulin drugs to inhibit motility, we suggest that the inhibitory effects of calcium on flagellar motility may be mediated in part by calmodulin. We conclude that the regulation of flagellar motility in cAMP and calcium includes mechanisms involving the control of the phosphorylation state of sperm proteins, some of which may be axonemal components.
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