title: The influence of storage temperature on the transition, activation enthalpy, and activity of enzymes associated with inner mitochondrial membranes.
abstract: 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.
authors.affiliation: Plant Physiology Group, CSIRO Division of Food Research, Macquarie University, NSW, Australia.
authors.forename: M A
authors.initials: MA
authors.lastname: Brown
authors.forename: J K
authors.initials: JK
authors.lastname: Raison
mesh_terms: 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
chemical_list: D009840:Oligomycins; D010088:Oxidoreductases; D013384:Succinate Cytochrome c Oxidoreductase; D006884:Hydroxybutyrate Dehydrogenase; D003576:Electron Transport Complex IV; D017301:Ca(2+) Mg(2+)-ATPase