Mode of inhibitory action of bilirubin on protein kinase C.
Ca2+-activated, phospholipid-dependent protein kinase (protein kinase C) is widely distributed in mammalian tissues. Accumulating evidence has revealed that protein kinase C as well as cAMP-dependent protein kinase plays important roles in various cellular functions. The purpose of this study is to examine the effect of bilirubin on protein kinase C and cAMP-dependent protein kinase activity in a cell-free system as a cause of bilirubin toxicity to the central nervous system. Bilirubin inhibited protein kinase C activity in a dose-dependent manner. This effect was markedly diminished by the addition of human serum albumin at a molar ratio of bilirubin to albumin of less than 1.0. Kinetic analysis revealed that bilirubin did not compete with phospholipid, diacylglycerol, or calcium. Bilirubin also inhibited cAMP-dependent protein kinase, but did not compete with cAMP. The inhibitory effect of bilirubin on protein kinase C seems to be irreversible because removal of bilirubin by Sephadex G-25 column chromatography did not restore the protein kinase C activity. Observations reported herein suggest that bilirubin, especially in its free form, induces an irreversible change to the catalytically active site of protein kinase C.
Sano
K
K
Nakamura
H
H
Matsuo
T
T
D000818:Animals; D001663:Bilirubin / Q000494:pharmacology*; D001921:Brain / Q000201:enzymology; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D066298:In Vitro Techniques; D011493:Protein Kinase C; D047428:Protein Kinase Inhibitors; D051381:Rats
D047428:Protein Kinase Inhibitors; D000242:Cyclic AMP; D011493:Protein Kinase C; D001663:Bilirubin; D002118:Calcium