PROTEIN-KINASE-C FROM BAT BRAIN - THE ENZYME FROM A HIBERNATING MAMMAL

Protein kinase C (PKC) from brain of euthermic and hibernating bats (M yotis lucifugus) showed only one form as determined by hydroxylapatite chromatography, compared with three forms found in rat brain. Cross-r eaction with antibodies to rabbit alpha, beta, and gamma isozymes show ed that bat brain contained only PKC(gamma). During hibernation the ac tivity of PKC in bat brain decreased to 63% of the euthermic value but the percentage that was membrane-associated did not change. Bat and r at brain PKC(gamma) were purified to homogeneity. Both enzymes phospho rylated all three of the substrates tested (FKKSFKL-NH2 peptide substr ate, histone H1, protamine), the bat enzyme having significantly highe r K-m values than rat PKC for both peptide and histone. Both enzymes r equired phospholipids and Ca2+ for activation with rat brain PKC depen ding almost exclusively on phosphatidylserine. Bat PKC, however, made use of other phospholipids and showed relative activities of 100:81:33 :42 for euthermic PKC and 100:91:45:35 for hibernator PKC with phospha tidylserine, phosphatidylinositol, phosphatidylcholine, and phosphatid ylethanolamine (each at 50 mu M), respectively. Activation of bat PKC by phosphatidylserine was temperature sensitive, being 3.5-fold at 4 d egrees C (hibernating body temperature) compared with 14-18-fold at 33 degrees C (near euthermic body temperature). Arrhenius plots for bat brain PKC showed a sharp break below 10 degrees C; activation energies below this temperature were 11.5- and 5.2-fold greater than at higher temperatures for the enzyme from hibernating versus euthermic animals . By contrast, plots for the rat enzyme were linear over the range 0-4 2 degrees C. The data suggest that a sharp suppression of PKC activity by several mechanisms (reduced total activity, low temperature effect s on activity and sensitivity to phospholipids) may be important to ov erall metabolic rate suppression during hibernation. (C) 1997 Elsevier Science Ltd.