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 °C)- and cold (7 °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 hind-brain, 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 Km for ATP, the Ka for Ca2+ or the Ka for phosphatidylserine were observed.