Dephosphorylation of a 30-kDa Protein of Fowl Spermatozoa by the Addition of Myosin Light Chain Kinase Substrate Peptide Inhibits the Flagellar Motility

Abstract

Phosphorylation of demembranated fowl sperm proteins during incubation with [γ- 32P]ATP and various protein kinase substrate peptides at 30°C was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A marked difference in phosphorylation was observed in a 30 kDa protein. This protein was strongly phosphorylated after the addition of Kemptide, a cAMP-dependent protein kinase (PKA) substrate peptide; Syntide 2, a calmodulin-dependent protein kinase II substrate peptide; a protein kinase C (PKC) substrate peptide; as well as control samples but only slightly phosphorylated in the presence of a myosin light chain kinase (MLCK) substrate peptide. The motility of demembranated spermatozoa at 30°C remained high in control samples and following the addition of Kemptide, Syntide 2 and PKC substrate peptide, but decreased markedly following the addition of MLCK substrate peptide. These results suggest that the 30 kDa protein is identified as a substrate for MLCK or a MLCK-like protein in fowl spermatozoa and that phosphorylation-dephosphorylation of this protein is involved in the regulation of flagellar movement at 30°C.