Protein kinases in rat testes. Subcellular distribution of the enzyme and endogenous substrates

The subcellular distribution of cAMP dependent and independent protein kinases (Pr K) has been studied in rat tests. The enzymatic activity was preferentially located in the cytosol. In all fractions mature animals have higher specific activity. The localization of endogenous protein substrates of Pr K was investigated using cytosol as an enzymatic source. The best endogenous substrate for the cAMP dependent Pr K seemed to be localized in the microsomal fraction. The rate of protein phosphorylation in the testicular subcellular fractions was examined by in vitro incubation with 32P-orthophosphate. The nuclear fractions have the highest specific radioactivity.