Protein kinase C and its endogenous substrate proteins in bovine mammary gland

Protein kinase C activity was evaluated and its endogenous substrate proteins were explored in bovine mammary gland. Activity was detected in both cytosolic and particulate fractions. However, the activity was more abundant in particulate than in cytosolic fractions. By gradient elution (0 to .5 M NaCl) of the enzyme from a DEAE-cellulose column, cytosolic enzyme was eluted at about .2 M NaCl, and particulate enzyme was eluted at .3 to .5 M NaCl, suggesting that the particulate enzyme was different from the cytosolic enzyme. At least four proteins (52, 43, 41, and 35 kdal) were demonstrated for the substrates of the enzyme in the gland. Two (52 and 43 kdal) of the four proteins were mainly detected in particulate fraction, whereas the 35-kdal protein was in cytosolic fraction and the 41-kdal protein was equally distributed in both fractions.