Structural and Functional Properties of Glycerol-3-Phosphate Dehydrogenase from a Mammalian Hibernator
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Glycerol-3-phosphate dehydrogenase (G3PDH; E.C.220.127.116.11) was purified from liver and skeletal muscle of black-tailed prairie dogs (Cynomys ludivicianus), a hibernating species. Native and subunit molecular masses of the dimeric enzyme were 77 and 40 kD, respectively, and both tissues contained a single isozyme with a pI of 6.4. Kinetic parameters of purified G3PDH from prairie dog liver and muscle were characterized at 22 and 5 °C and compared with rabbit muscle G3PDH. Substrate affinities for hibernator muscle G3PDH were stable (NAD) or increased significantly (Km G3P and DHAP decreased) at low temperature whereas Km NAD and DHAP of rabbit G3PDH increased. Prairie dog G3PDH showed greater conservation of Km G3P over a wide temperature range as well as greater thermal stability and resistance to chemical denaturation by guanidine hydrochloride than the rabbit enzyme. In addition, using the protein sequence of the hibernating thirteen-lined ground squirrel (Ictidomys tridecemlineatus) and bioinformatics tools, the deduced protein structure of G3PDH was compared between heterothermic and homeothermic mammals. Structural and functional characteristics of G3PDH from the hibernating species would support enzyme function over a wide range of core body temperatures over cycles of torpor and arousal.
KeywordsTorpor Gluconeogenesis from glycerol Fluorescence characterization Temperature effects on kinetic parameters Thermal stability
High performance liquid chromatography
Sodium dodecyl sulfate polyacrylamide gel electrophoresis
We thank Henry J. Harlow, University of Wyoming for providing the prairie dog tissue samples for this study. Thanks also to J. M. Storey for critical commentary on the manuscript. Supported by a research grant from the N.S.E.R.C. Canada to KBS. SNT held a NSERC PGSD scholarship.
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