Reversible association of ox liver glutamate dehydrogenase with the inner mitochondrial membrane.

A comparative study on the catalytic and allosteric properties of particulate and soluble forms of ox liver glutamate dehydrogenase has been carried out. The response of the bound enzyme to release by various effectors was investigated. The particulate enzyme was found to have catalytic activities similar to the free enzyme in contrast to its behaviour when bound to pure anionic phospholipids. Possible reasons for such outstanding differences are discussed.

Arrhenius plots of membrane-bound enzymes of mitochondria and microsomes in the brain cortex of developing and old rats.

To study changes in lipid-protein-interaction and fluidity in mitochondrial and microsomal membranes of brain during development and aging, the Arrhenius plots of marker enzymes for mitochondrial inner and outer membranes as well as those of microsomal membranes were compared at different ages. The enzymes were, beta-hydroxybutyrate dehydrogenase (BDH) for the inner mitochondrial membrane and rotenone-insensitive-NADH-cytochrome c reductase (Mit-NADH-CytR) for the outer membrane; also antimycin-insensitive-NADH-cytochrome c reductase (Micr-NADH-CytR) and NADPH-cytochrome c reductase for the microsomal membranes. The ages studied were, 1, 5, 30, 60 days postnatal and 2 years. In the microsomes, the plots of NADH-cytochrome c reductase were found to be biphasic at all ages except in the newborn where no break temperature was observed. The activation energy of this enzyme in the physiological range of temperature was found to be high in the newborn, declining with brain maturation. The plot of this enzyme in the old rat showed no difference when compared with the mature. The specific activity of the enzyme, however, was markedly reduced in the old brain microsomal fraction. In contrast, comparison of the plots of microsomal NADPH-cytochrome c reductase at the various ages revealed no break temperature and very similar energies of activation. For the inner mitochondrial membrane beta-hydroxybutyrate dehydrogenase, the Arrhenius plots were generally biphasic at all ages studied with a break temperature of about 20 degrees C. However, the newborn plot was only barely biphasic showing a high energy of activation in the physiological range of temperature. In contrast, for the outer membrane NADH-cytochrome c reductase, the newborn plots were definitely biphasic, exhibiting low activation energy above the breaks. There was also a significant decline in the break temperature with brain development. No significant differences in the plots of this enzyme were found between the old and mature brain cortex. It is concluded that the enzymes of inner and outer mitochondrial membranes as well as the oxidative enzymes of microsomal membranes may show differential patterns of change in lipid-protein-interaction during development and aging, the changes being more marked in development than in aging.