PROTEIN KINASE C FROM BAT BRAIN: THE ENZYME FROM A HIBERNATING MAMMAL
Section snippets
INTRODUCTION
The Ca2+-activated and phospholipid-dependent protein kinase, also known as protein kinase C (PKC) has been implicated in the regulation of many cellular functions (Nishizuka (1988), Nishizuka (1992)). PKC distribution between cytosolic and membrane fractions is dependent upon physiological state and the tissue source. Hormones, growth factors and tumour-promoting phorbol esters can cause the translocation of PKC from cytosol to membrane (Kraft and Anderson, 1983; Farrar and Anderson, 1985;
Chemicals and animals
[γ-32P]ATP (3000 Ci/mmol) was obtained from New England Nuclear (Montreal, Canada). All phospholipids, 1,2-dioleoylglycerol, and fatty acids were obtained from Serdary Research Laboratories (London, ON, Canada). Phosphocellulose (P81) was obtained from Whatman (Canlab Corp., Mississauga, ON, Canada); nitrocellulose sheets were from Schleicher and Schuell (Keene, NH, U.S.A.). Peptide substrate was a generous gift from Dr J.P. Durkin, Institute of Biological Research, National Research Council,
PKC activities, isoforms and translocation in bat brain
Table 1 shows the activities of PKC in brain of euthermic (control) vs hibernating bats. The total PKC activity in brain of euthermic bats (cytosolic + membrane-associated, assayed with peptide as substrate) was significantly higher than in brains of hibernating animals, 6540 vs 4096 pmol/gram wet mass, but the percentage of the enzyme that was membrane-associated (17–18%) was the same in both groups.
Preliminary analysis of the PKC types present in bat brain extracts was made using
DISCUSSION
The data presented address three different modes of adaptive regulation that could be used to modify PKC function to benefit mammalian hibernation. These are: (1) species-specific differences between the enzyme from a hibernating and a non-hibernating mammal; (2) changes in enzyme properties in vivo between the euthermic and hibernating states; and (3) temperature effects on enzyme properties. The data give evidence that all three of these modes of regulation contribute PKC control in bat brain.
Acknowledgements
Thanks to Dr D.W. Thomas, University of Sherbrooke for providing bats and hibernation facilities, to J.A. Duncan for determinations of Km Mg.ATP, and to J.M. Storey for critical commentary on the manuscript. Supported by operating grants from the N.S.E.R.C. Canada and the N.I.H. (GM 43796) to K.B. Storey.
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Present address: Department of Biochemistry, Bagheiatollah Medical Science University, 3 Rah Arag, Aghdasseih, Tehran, Iran.