The influence of storage temperature on the transition, activation enthalpy, and activity of enzymes associated with inner mitochondrial membranes.
The effects of storage at low temperature on the transition in enzyme function, Tf*, and the Arrhenius activation energy, Ea, were determined for several enzymes associated with the inner membrane of rat liver mitochondria. The enzymes studied were succinate:cytochrome c reductase, cytochrome c oxidase, beta-hydroxybutyrate dehydrogenase, and oligomycin-sensitive, Mg2+-activated ATPase. For freshly isolated mitochondria the Tf*, for succinate:cytochrome c reductase and cytochrome c oxidase, occurred at approximately 23 degrees C and was coincident with a transition in structure, Ts*, determined as the change in temperature coefficient of motion for a spin label intercalated with the membrane lipids. This suggest that the change in thermal response of the membrane-associated enzymes is related to a change in molecular ordering of the membrane lipids. When mitochondria were stored at -12 degrees C, the specific activities of succinate:cytochrome c reductase and cytochrome c oxidase decreased. Concomitant with these changes the Ea, above Tf*, increased. After 100 days storage at -12 degrees C, Ea above Tf* approached the value for Ea below Tf* such that the transition in thermal response could no longer be detected. In contrast, for mitochondria stored at -196 degrees C, although the specific activity declined over the 100 days storage, no changes in either Ea or Tf* were evident. The results indicate a need for caution in evaluating comparative studies of Tf and Ea, for membrane-associated enzymes, using mitochondria which have been frozen and stored.
Brown
M A
MA
Plant Physiology Group, CSIRO Division of Food Research, Macquarie University, NSW, Australia.
Raison
J K
JK
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D004789:Enzyme Activation; D005615:Freezing; D006884:Hydroxybutyrate Dehydrogenase / Q000378:metabolism*; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D008930:Mitochondria, Liver / Q000201:enzymology*; D009840:Oligomycins / Q000494:pharmacology; D010088:Oxidoreductases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013384:Succinate Cytochrome c Oxidoreductase / Q000378:metabolism*; D013816:Thermodynamics
D009840:Oligomycins; D010088:Oxidoreductases; D013384:Succinate Cytochrome c Oxidoreductase; D006884:Hydroxybutyrate Dehydrogenase; D003576:Electron Transport Complex IV; D017301:Ca(2+) Mg(2+)-ATPase