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[Oxidative phosphorylation, NADH-oxidase and succinate oxidase activity in testicular mitochondria of rats with alloxan diabetes].

Decrease in V4P, V3 and VP, in coefficient of respiratory control, in the ratio ADP:0 as well as an increase in duration of phosphorylation of ADP involved in oxidation of succinate were found in testes mitochondria from rats with alloxan diabetes (content of glucose 20 +/- 2 mmol/L in blood plasma). If a mixture of malate and glutamate was used as a substrate of oxidation, the rate of mitochondrial respiration and coefficient of respiratory control were decreased in testes of diabetic rats under conditions of all the metabolic states studied. At the same time, sensitivity of NADH-oxidase and succinate oxidase systems to controlled heating (28 degrees) was distinctly decreased in the testes mitochondrial membranes of the impaired animals as compared with controls. The data obtained suggest that distinct functional and, apparently, structure alterations occurred in the testes mitochondrial membranes of rats with alloxan diabetes.

Animals↗
PubMed1973

Succinate oxidase in Neurospora.

Two kinetically distinct states of succinate oxidase have been detected in the mitochondria of Neruospora crassa. One state has a K(m) for succinate of 4.1 x 10(-3)m, and the other has a K(m) for succinate of 3.5 x 10(-4)m. The high K(m) state was found in freshly extracted mitochondria from either 20- or 72-hr mycelium. However, the succinate oxidase activity in mitochondria from 20-hr mycelium rapidly deteriorated in vitro, leaving a stable residual activity with the lower K(m) for succinate. Adenosine triphosphate (ATP) plus Mg(2+) stabilized the high K(m) state in these preparations. The high K(m) state of succinate oxidase was further characterized by a two- to threefold increase in activity over the pH range 6.6 to 8.0 and by classical competitive inhibition by fumarate and malonate. By contrast, the low K(m) state of succinate oxidase showed a relatively flat response to pH over the range 6.6 to 8.0 and a nonclassical pattern of inhibition by fumarate and malonate, as shown by nonlinear plots of reciprocal velocity versus reciprocal substrate concentration in the presence of inhibitor or reciprocal velocity versus inhibitor concentration at fixed substrate concentrations. The relationship of mycelial age to the in vitro stability of succinate oxidase is considered with reference to probable changes in the relative pool sizes of extra- and intramitochondrial ATP in response to changes in the rate of glycolysis.

Adenosine Triphosphate↗