Isolation and properties of a protein complex containing flagellar movement-initiating phosphoprotein from testes of a white salmon.

Phosphorylation of a tyrosine residue within a 15-kDa protein has been found to play a role in the initiation of flagellar movement of quiescent spermatozoa of the rainbow trout, Salmo gairdneri [Morisawa & Hayashi (1986) Biomed. Res. 6, 181-184; Hayashi et al. (1987) J. Biol. Chem. 262, 16692-16698]. In order to find a more accessible source of the 15-kDa protein for biochemical studies, phosphorylation of proteins was studied in other organs from other species. Cell-free extracts from spermatozoa and testes of Salmonidae were prepared and all catalyzed the cAMP-dependent, Mg(2+)-requiring, but Ca(2+)-independent phosphorylation of the 15-kDa proteins. Protein from the testes of a white salmon, Oncorhynchus keta, was isolated by conventional purification methods. The 15-kDa protein in the cell-free extract was found to be complexed with several other proteins such that the 15-kDa protein and its phosphorylating activity were copurified. Isolation of a sufficient amount of the complex for the preparation of antibodies against the various constituents is now possible.