Interrelationship in the regulation of pyruvate dehydrogenase and adenine-nucleotide translocase by palmitoyl-CoA in isolated mitochondria

The "B space" of mitochondrial phosphorylation

It was recently shown that, in progressively depolarizing mitochondria, the F(0) -F(1) ATP synthase and the adenine nucleotide translocase (ANT) may change directionality independently from each other (Chinopoulos et al. [2010] FASEB J. 24:2405). When the membrane potentials at which these two molecular entities reverse directionality, termed reversal potential (Erev), are plotted as a function of matrix ATP/ADP ratio, an area of the plot is bracketed by the Erev_ATPase and the Erev_ANT, which we call "B space". Both reversal potentials are dynamic, in that they depend on the fluctuating values of the participating reactants; however, Erev_ATPase is almost always more negative than Erev_ANT. Here we review the conditions that define the boundaries of the "B space". Emphasis is placed on the role of matrix substrate-level phosphorylation, because during metabolic compromise this mechanism could maintain mitochondrial membrane potential and prevent the influx of cytosolic ATP destined for hydrolysis by the reversed F(0) -F(1) ATP synthase.

Modeling of ATP-ADP steady-state exchange rate mediated by the adenine nucleotide translocase in isolated mitochondria

A computational model for the ATP-ADP steady-state exchange rate mediated by adenine nucleotide translocase (ANT) versus mitochondrial membrane potential dependence in isolated rat liver mitochondria is presented. The model represents the system of three ordinary differential equations, and the basic components included are ANT, F(0)/F(1)-ATPase, and the phosphate carrier. The model reproduces quantitatively the relationship between mitochondrial membrane potential and the ATP-ADP steady-state exchange rate mediated by the ANT operating in the forward mode, with the assumption that the phosphate carrier functions under rapid equilibrium. Furthermore, the model can simulate the kinetics of experimentally measured data on mitochondrial membrane potential titrated by an uncoupler. Verified predictions imply that the ADP influx rate is highly dependent on the mitochondrial membrane potential, and in the 0-100 mV range it is close to zero, owing to extremely low matrix ATP values. In addition to providing theoretical values of free matrix ATP and ADP, the model explains the diminished ADP-ATP exchange rate in the presence of nigericin, a condition in which there is hyperpolarization of the inner mitochondrial membrane at the expense of the mitochondrial Delta pH gradient; the latter parameter influences matrix inorganic phosphate and ATP concentrations in a manner also described.

Brain pyruvate and 2-oxoglutarate dehydrogenase complexes are mitochondrial targets of the CoA ester of the Refsum disease marker phytanic acid

Pyruvate and 2-oxoglutarate dehydrogenase complexes are strongly inhibited by phytanoyl-CoA (IC(50) approximately 10(-6)-10(-7) M). Palmitoyl-CoA is 10-fold less potent. Phytanic or palmitic acids have no inhibitory effect up to 0.3 mM. At the substrate saturation, the acyl-CoA's affect the first and second enzymatic components of the 2-oxoglutarate dehydrogenase complex, while the third component is inhibited only at a low saturation with its substrate dihydrolipoamide. Thus, key regulatory branch points of mitochondrial metabolism are targets of a cellular derivative of phytanic acid. Decreased activity of the complexes might therefore contribute to neurological symptoms upon accumulation of phytanic acid in Refsum disease.

Effects of high fat-feeding to rats on the interrelationship of body weight, plasma insulin, and fatty acyl-coenzyme A esters in liver and skeletal muscle

Rats fed a high-saturated fat diet consumed more energy, gained more weight, and displayed hyperinsulinemia (P less than .05) without an elevation in the fasting plasma glucose level, compared with animals on two different high-carbohydrate diets. The total fatty acyl-coenzyme A (CoA) concentration was 18% (P less than .0001) and 46% (P less than .0001) higher in liver and skeletal muscle, respectively, from rats fed the high-fat diet compared with each of the other diet groups. Major long-chain fatty acyl-CoA molecular species of both tissues in high fat-fed rats reflected the fatty acid profile of the diet. Approximately 29%, 21%, and 16% of total liver and skeletal muscle fatty acyl-CoAs were comprised of oleoyl-CoA, palmitoyl-CoA, and stearoyl-CoA, respectively. The amounts of these three fatty acyl-CoA esters were significantly higher in liver and skeletal muscle after high-fat feeding than with the other diet treatments (P less than .0001). In contrast, the concentration of linoleoyl-CoA was lower in both tissues after high-fat feeding (P less than .0001). In rats fed the high-fat diet, plasma insulin levels were significantly correlated with gain in body weight or body weight (r = .80, P less than .001 for insulin and gain in body weight; r = .73, P less than .001 for insulin and body weight). Total fatty acyl-CoA ester content in liver and skeletal muscle was also strongly correlated with the plasma insulin concentration in high fat-fed rats (r = .80, P less than .001 for liver; r = .78, P less than .001 for skeletal muscle).(ABSTRACT TRUNCATED AT 250 WORDS)

The modes of action of long chain alkyl compounds on the respiratory chain-linked energy transducing system in submitochondrial particles

The interactions of long chain (greater than C7), alkyl compounds with tightly coupled, beef heart submitochondrial particles (SMP) have been investigated with respect to their effects upon respiratory chain-linked electron transfer and energy coupling capacity. Long chain alkyl alcohols, amines, free fatty acids, and methyl esters exhibit a general uncoupling effect, with stimulation of the succinate oxidase activity but inhibition of the NADH oxidase, in SMP. The degree of effectiveness is dependent on the nature of the functional group and the length of the alkyl chain. Submitochondrial particles depleted of F1 and the F1-inhibitor protein are similarly affected. Subsequent treatment with bovine serum albumin reverses the effects of free fatty acids and results in partial recovery of activity with alkyl amines, alcohols, and methyl esters. Differences between the effects of these alkyl compounds and those of sodium dodecyl sulfate, deoxycholate, palmitoyl carnitine, and palmitoyl CoA rule out detergent-like action as the explanation for these observations. These data suggest that specific lipophilic interactions with the membrane, modulated by the nature of the functional group, are responsible for the effects of these compounds on the energy transducing system of SMP. Analyses of the reduction kinetics of the cytochromes indicate that the sites of interaction of these compounds with the inner mitochondrial membrane are associated with the primary dehydrogenase of complex I and energy coupling site 2; alkyl amines possess an additional site of interaction in the region of complex III.

Investigations into the direct effects of insulin on hepatic ketogenesis, lipoprotein secretion and pyruvate dehydrogenase activity

In the rat liver perfused with whole rat blood containing either decreased or increased concentrations of non-esterified fatty acids, insulin decreased production of acetoacetate and 3-hydroxybutyrate and stimulated secretion of very-low-density-lipoprotein triacylglycerol. In these same livers, pyruvate dehydrogenase activity was not altered by insulin addition, although it was diminished by non-esterified fatty acids.