Involvement of tyrosine protein kinase in the initiation of flagellar movement in rainbow trout spermatozoa.

Initiation of flagellar motility in spermatozoa of the rainbow trout, Salmo gairdneri, is closely related to phosphorylation of a protein of molecular mass 15 kDa (Morisawa, M., and Hayashi, H. (1986) Biomed. Res. 6, 181-184). We have been able to solubilize the protein and its kinase and then construct an assay system in vitro for the phosphorylation of the 15-kDa protein. In vitro, the protein was phosphorylated in a cAMP-dependent manner. The phosphorylation absolutely required the presence of Mg2+ ions. at millimolar concentrations, but not of Ca2+ ions. The amino acid residue which was phosphorylated in the 15-kDa protein was tyrosine. The 15-kDa protein was purified to near homogeneity by affinity chromatography on a column of adenosine nucleotides conjugated to Eupergit and ion-exchange chromatography on DEAE-cellulose. The effects of synthetic inhibitors of protein kinase on the phosphorylation of the 15-kDa protein were also studied.