Acid Oxidation System Research Articles

Degradation of matacil by the ascorbic acid oxidation system.

Degradation of matacil by the ascorbic acid oxidation system.

Rates of Oxidation of Different Fatty Acids by Isolated Rat Liver Mitochondria

The oxidation rates for palmitic, stearic, oleic, and linoleic acids as their albumin complexes and for caprylic, butyric, and acetic acid as their potassium salts with isolated rat liver mitochondria were studied in a system where it had previously been demonstrated that the respiratory chain and the coupling of phosphorylation to oxidation is intact even at high concentrations of long chain fatty acids. Results were obtained which apparently fitted the Michaelis-Menten equation. The values of Km decreased with increasing length of the carbon chain. Of the long chain fatty acids, linoleic acid has the lowest constant. Vmax for long chain fatty acids was highest for linoleic acid, but this value was not as high as those of short chain fatty acids. However, if different substrates were compared in terms of the product nVmax, where n is the number of carbon atoms in the fatty acid, linoleic acid shows as high values as short chain fatty acids. The possibility is discussed that linoleic acid has the highest affinity for the mitochondrial fatty acid oxidation system and that it is oxidized at the fastest rate of the long chain fatty acids studied. Implications of this findings for previously observed differences in fatty acid metabolism in vivo, explainable by increased linoleic acid oxidation, are considered.

Changes in the ascorbate concentration of pinto bean leaves accompanying the formation of TMV-induced local lesions

Abstract The concentration of ascorbic acid in Pinto bean half-leaves was followed from the time of inoculation with TMV to the time of appearance of the local lesions. In all cases there was a rise following inoculation relative to the zero time concentration and to the concentration in the opposite, half-leaf controls. This was followed by a rapid decrease in concentration so that by the time of local lesion appearance it was always considerably less than in the control half-leaves. This pattern of change occurred whether the lesions first appeared in 21 or 48 hours and whether plants were incubated in the greenhouse or in a light chamber under continuous illumination. Half-leaves wounded with Carborundum showed a similar but less striking pattern of change in ascorbic acid concentration in some experiments. In others the pattern of change was almost identical to the untreated, control half-leaves or leaves on untreated plants. Where dehydroascorbic acid as well as ascorbic acid concentration was determined in the same tissue, the former followed an inverse pattern of change with time to that of ascorbic acid. In infected leaves the rapid decrease in ascorbate was approximately stoichiometrically equivalent to the increase in dehydroascorbate concentration. This suggested an activation by the infection of an ascorbic acid oxidation system. From the timing of these events it is suggested that the events responsible for virus localization precede those associated with the virus-induced ascorbic acid oxidation and lesion appearance.

The Oxidation of Fatty Acids Combined with Albumin by Isolated Rat Liver Mitochondria

Long chain fatty acids at concentrations inhibiting mitochondrial respiration were, in the presence of serum albumin, found to produce almost as high a rate of oxygen uptake as alpha-ketoglutarate, succinate, or acetate. This oxidation was characterized in terms of its coupling to phosphorylation, need for cofactors, and production of different metabolites during the reactions. Fatty acids were oxidized to carbon dioxide, acetoacetate, beta-hydroxybutyrate, and other water-soluble metabolites, tentatively identified as intermediates of the citric acid cycle. An agent to spark the citric acid cycle and adenosine tri- or monophosphate were necessary for optimal oxidation rate, as described for other fatty acid oxidation systems. Balance experiments with different amounts of malate were performed with incubations lasting as long as oxygen uptake took place. In the presence of 1 mumole of malate, practically all added palmitic acid was used up and found to be converted primarily to carbon dioxide, acetoacetate, and other water-soluble metabolites of which the major part was tentatively identified as succinate. A significant portion was found in mitochondrial phospholipids. With 10 mumoles of malate some palmitic acid remained in the system, while a comparatively small amount was converted to carbon dioxide, and a major part was found as succinate. Here also incorporation into phospholipids occurred. With no malate added, fatty acid oxidation was much smaller than with malate, although significant conversion to carbon dioxide took place. Only a little succinate and phospholipid were found. Oxygen uptake was greater than a theoretical value calculated from radioactive balance experiments. It was concluded that albumin contains oxidizable material even after extraction and dialysis. Albumin at high concentrations inhibited both fatty acid and alpha-ketoglutarate oxidation. The oxidation of long chain fatty acids in high concentrations in the form of albumin-fatty acid complex was coupled to phosphorylation. Thus P:O ratios above 2 were found as well as evidence for respiratory control. It was concluded that oxidation of long chain fatty acids by isolated mitochondria occurs from their albumin complex. This process can also be studied at high concentrations of fatty acids, where high rates of oxygen uptake are obtained from oxidation which is coupled to phosphorylation.

Relative distribution of the mitochondria in the two types of fibres in the pectoralis major muscle of the pigeon.

IT has been noted that the pectoralis major muscle of the pigeon consists of two types of fibres, one of them a white, broad and glycogen-loaded variety, and the other red, narrow and fat-loaded1, and that the lipase activity is much greater in the latter than in the former2. Recent studies conducted in our laboratories3,4 suggest the presence of a well-organized fatty acid oxidation system in the breast muscle of flying birds. Since the mitochondria are known to be the seat of oxidative processes, it was thought desirable to study the relative distribution of the mitochondria in the two types of fibres in the pectoralis major muscle of the pigeon.