PROTEIN-KINASE-C IN TURTLE BRAIN - CHANGES IN ENZYME-ACTIVITY DURING ANOXIA

Protein kinase C from the anoxia-tolerant turtle Pseudemys scripta elegans was investigated to determine its role in mediating changes in brain metabolism associated with anoxia. Measurements of protein kinase C distribution in cytosol and membrane-associated fractions of cerebrum and hindbrain were performed with warm (18-degrees-C)- and cold (7-degrees-C)-acclimated animals exposed to normoxic or anoxic conditions. In cerebrum, the percentage of bound protein kinase C decreased from 48.5% to 35.1% in warm-acclimated animals and from 45.0% to 25.6% in cold-acclimated animals. In the hindbrain, bound protein kinase C increased from 45.0% to 72.9% in warm-acclimated animals and from 40.3% to 68.8% in cold-acclimated animals. The presence of three distinct protein kinase C isozymes (Types I, II and III) was confirmed by hydroxylapatite chromatography. The distribution of isozymes between cytosolic and membrane-associated fractions in cerebrum was 24% I, 37% II and 39% III (cytosolic) and 32% I, 35% II and 34% III (membrane-associated). In the hindbrain, the protein kinase C isozyme distribution was 34 % I, 40 % II and 26 % III (cytosolic) and 18 % I, 47 % II and 35 % III (membrane-associated). Kinetic characterization of the three isozymes showed that Type I was 27% activated by Ca2+, whereas Types II and III were only 4% and 2% activated by Ca2+, respectively. Full activity for all enzymes was observed only in the presence of phosphatidylserine and diacylglycerol. No differences in the K(m) for ATP, the K(a) for Ca2+ or the K(a) for phosphatidylserine were observed.