Insulin-status-dependent modulation of FoF1 ATPase activity in rat kidney mitochondria

Altered Kinetics Properties of Erythrocyte Lactate Dehydrogenase in Type II Diabetic Patients and Its Implications for Lactic Acidosis

Recent studies have been noted that the erythrocytes from Type II diabetic patients show significantly altered structural and functional characteristics along with the changed intracellular concentrations of glycolytic intermediates. More recent studies from our laboratory have shown that the activities of enzymes of glycolytic pathway changed significantly in RBCs from Type II diabetic patients. In particular the levels of lactate dehydrogenase (LDH) increased significantly. Lactic acidosis is an established feature of diabetes and LDH plays a crucial role in conversion of pyruvate to lactate and reportedly, the levels of lactate are significantly high which is consistent with our observation on increased levels of LDH. Owing to this background, we examined the role of erythrocyte LDH in lactic acidosis by studying its kinetics properties in Type II diabetic patients. Km, Vmax and apparent catalytic efficiency were determined using pyruvate and NADH as the substrates. With pyruvate as the substrate the Km values were comparable but Vmax increased significantly in the diabetic group. With NADH as the substrate the enzyme activity of the diabetic group resolved in two components as against a single component in the controls. The Apparent Kcat and Kcat/Km values for pyruvate increased in the diabetic group. The Ki for pyruvate increased by two fold for the enzyme from diabetic group with a marginal decrease in Ki for NADH. The observed changes in catalytic attributes are conducive to enable the enzyme to carry the reaction in forward direction towards conversion of pyruvate to lactate leading to lactic acidosis.

Thyroid Hormone-Induced Alterations in Membrane Structure-Function Relationships: Studies on Kinetic Properties of Rat Kidney Microsomal Na+,K+-ATPase and Lipid/Phospholipid Profiles

The effects of thyroidectomy (Tx) and subsequent treatment with 3,5,3'-triiodothyronine (T(3)) or combined replacement therapy (T(R)) with T(3 )and thyroxine (T(4)) on the substrate and temperature kinetics properties of Na+,K+-ATPase and lipid/phospholipid makeup of rat kidney microsomes were examined. Enzyme activity was somewhat high in the hypothyroid (Tx) animals and increased significantly following T(3) treatment, while T(R) treatment caused a decrease. In the Tx and T(3) groups enzyme activity resolved in two kinetic components, while in the T(R) group the enzyme showed allosteric behavior up to 0.5 mM: ATP concentration. The K(m) and V(max) values of both the components decreased in Tx animals without affecting the catalytic efficiency. T(3) treatment caused a significant increase in the V(max) of both the components, with a significant increase in the catalytic efficiency, while the K(m) values were not upregulated. The T(R) regimen lowered the K(m) and V(max) of component II but improved the catalytic efficiency. Thyroid status-dependent changes were also noted in the temperature kinetics of the enzyme. Regression analysis revealed that changes in the substrate and temperature kinetics parameters correlated with specific phospholipid components.

Diabetic modulation of the temperature kinetics properties of cytochrome oxidase activity in rat brain mitochondria

The effects of alloxan-diabetes and subsequent treatment with insulin on temperature kinetics properties of cytochrome oxidase activity from rat brain mitochondria were examined. The enzyme activity decreased only at the late stage of diabetes which was not normalized by insulin treatment; however at early stage of diabetes hyper-stimulation occurred. In the control animals the Arrhenius plot was chair shaped with three energies of (E1, E2 and E3) and two phase transition temperatures (Tt1 and Tt2). At early diabetic stage the Arrhenius plot became biphasic and E1)and E2 decreased; insulin treatment reversed chair-shaped pattern with increase in E2. These changes correlated with transient changes in the phospholipids profiles especially decreased acidic phospholipids. The temperature kinetics parameters were minimally affected at the late stage of diabetes or by insulin treatment. Thus at the late stage the brain tissue seems to have readjusted to its insulin homeostasis.

Effect of alloxan diabetes and subsequent insulin treatment on temperature kinetics properties of succinate oxidase activity in rat kidney mitochondria

Early and late effects of alloxan diabetes and subsequent treatment with insulin on the temperature kinetics properties of succinate oxidase (SO) activity in rat kidney mitochondria were examined. In diabetic animals SO activity increased significantly and the increase was more pronounced at the late stage. Insulin treatment partially restored SO activity. However, the effect was temperature-dependent. In diabetic animals the energy of activation in the low temperature range (E(L)) increased significantly while that in the high temperature range (E(H)) decreased. The latter seems to be responsible for improving catalytic efficiency in the diabetic state. Insulin treatment normalized E(H) only in the 1-month diabetic group. The phase transition temperature (Tt), decreased in diabetic animals. Insulin treatment caused an increase beyond the control value in Tt in 1-month diabetic animals. The results suggest that insulin status-dependent modulation of SO activity is a complex process.

Insulin status-dependent alterations in lipid/phospholipid composition of rat kidney microsomes and mitochondria

Early and late effects of alloxan-diabetes on lipid/phospholipid composition in rat kidney microsomes and mitochondria were examined. In microsomes, early diabetic state resulted in an increase in contents of total phospholipids (TPL), cholesterol (CHL), with an increase in the lysophospholipids (Lyso), phosphatidylcholine (PC), and phosphatidylinositol (PI) components. The sphingomyelin (SPM), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidic acid (PA) content decreased. Treatment with insulin had no effect on PC but PE increased and the other components decreased. In the 1-month diabetic group PI, PS, PE, and PA components decreased, whereas Lyso and PC increased. Treatment with insulin had restorative effects on PE, PI, and PS; Lyso was further elevated whereas PA decreased. In mitochondria, at an early stage of diabetes marginally increased CHL content was restored by insulin treatment. Long-term diabetes lowered the TPL and elevated the CHL content. Treatment with insulin partially restored the TPL and CHL content. A diabetic state decreased the proportion of PE and diphosphatidylglycerol (DPG) components but increased the Lyso, SPM, PC, PI, and PS components in the mitochondria. Treatment with insulin had a partial restorative effect. The membrane fluidity of both microsomes and mitochondria decreased in general in the diabetic condition and was not corrected by insulin treatment at a late stage. However, at an early stage, treatment with insulin fluidized both membranes.