Phospholipid-Sensitive Ca2+-Dependent Protein Kinase System in Testis: Localization and Endogenous Substrates*

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Abstract
The prsence 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 cytosol and matured spermatozoa obtained from the epididymis. At least 3 endogenous substrates (83,000, 33,000 and 26,000) and 5 substrates (> 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 3 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.