Phospholipid-sensitive Ca2+-dependent protein kinase system in testis: localization and endogenous substrates.

The presence and localization in pig and rat testes of phospholipid-sensitive Ca2+-dependent protein kinase (PL-Ca-PK) and its substrates were investigated. PL-Ca-PK activity was found in the testis total particulate fraction and epididymal fluid, but little in the testis total particulate fraction and epididymal fluid, but little in the testis cytosol and matured spermatozoa obtained from the epididymis. Similarly, at least three endogenous substrates (83,000, 33,000, and 26,000) and five substrates (greater than 100,000, 83,000, 60,000, 43,000, and 19,000) for PL-Ca-PK were detected in the testis total particulate fraction and the epididymal fluid, respectively, but little or no substrates were observed in the testis cytosol and matured spermatozoa. The three substrates detected in the total particulate fraction were also observed in the testis nuclear fraction. In rat testis, PL-Ca-PK activity was detected in the total particulate fraction of germ cells. The results suggested that PL-Ca-PK system might be important in membrane- or subcellular organellar-associated functions in testis.