Isocitric acid concentrations 358

Polarographic studies of a mitochondrial fraction from Hymenolepis diminuta showed that of four substrates tested, DL-glycerol-3-phosphate was the most rapidly oxidized, but the highest respiratory control ratio (1.7) was obtained with dl-isocitric acid. With isocitrate as substrate oxyclozanide at 1.61 nM stimulated O uptake and relieved oligomycin inhibition of adinosine diphosphate-stimulated respiration, but at concentrations above 2 pM progressively inhibited O uptake. Rafoxanide, niclosamide, 3,4,5-tribromo-salicylanilide, nitroxynil, resorantel, di-chlorophen, and 2,4-dinitrophenol exhibited effects similar to those of oxyclozanide on the respiration in cestode mitochondria. The relative potencies were compared and the possible mode of action discussed [38]. 

A subgroup of the German Chemical Society (173,174) recently published a system which proposed a means of evaluating the juice content of low-juice beverages. It is based on the concentrations of potassium, phosphorus, proline, formol number, isocitric acid and malic acid. Equations for the juice content of lemonades and orange juices (with possible mixture of tangerine or mandarin juice) based drinks are ... 

A reactor containing a Dean-Stark trap was charged with isocitric acid lactone (14.3 mmol), propanediol (15.7 mmol), and benzene was then refluxed at 90°C overnight. The mixture was concentrated and a viscous liquid isolated that solidified on cooling. 

Fluorimetric methods involving six dehydrogenases have been used to determine the concentrations of 21 of the more common organic acids (58). Sensitivity of the methods range from 0.02 fxg/m for determination of D-isocitric acid with isocitrate dehydrogenase to 200 /xg/ml for determination of D-tartaric acid with malate dehydrogenase. 

Aliphatic tricarboxylic acids such as citric acid exhibit a remarkably high affinity toward the stationary phase of an anion exchanger. Hence, low ionic strength bicarbon-ate/carbonate buffer solutions are not particularly suited as eluents. However, when a sodium hydroxide solution at a comparatively high concentration (c 0.08 mol/L) is used, citric acid may be eluted, and may even be separated from its structural isomer isocitric acid. When the detection of these compounds is carried out via electrical con-... 

This separation can also be achieved by chromatography on silica gel with such a method, Frohman et al. (F16) have found that the concentration of blood isocitric acid is less than 0.1 mg% in the rat. 

An isomer of citric acid is (1J ,2S)-1-hydroxypropan-1,2,3-tricarboxylic acid (8-67), also known as D-isocitric acid u-threo isomer), which is another intermediate of the citric acid cycle. This acid is the dominant acid in blackberries (Table 8.17) and occurs in other fruits in small or insignificant amounts (e.g. in apples). The isocitric acid content is one of the most important markers in the estimation of the proportion of fruit in coloured fruit mixtures, for example in mixtures of blackcurrants, strawberries and raspberries with apples. The concentration ratio of citric acid to isocitric acid is also employed for the detection of adulteration, and can reveal the addition of synthetic citric acid to optimise the taste of fruit drinks, especially in the case of added sugar. 

Several mutant strains of R. eutropha that were made to possess defective competing metabolic pathways with the PHA biosynthetic pathway were developed for the enhanced PHA production. The isocitrate dehydrogenase leaky mutant of R. eutropha accumulated P(3HB) more favorably at a lower car-bon/nitrogen molar ratio and at a lower carbon concentration than the parent strain [82]. In batch culture, the final cell and P(3HB) concentrations, and P(3HB) yield on glucose were slightly increased. Also, in the P(3HB-co-3HV) biosynthesis, the molar fraction of 3HV and the 3HV yield on propionic acid increased due to the enhanced conversion of propionic acid to 3-hydroxyvaleryl-CoA rather than to acetyl-CoA and C02 in this mutant. Another mutant R. eu-... 

In the presence of adequate O, the rate of oxidative phosphorylation is dependent on the availability of ADR. The concentrations of ADR and ATR are reciprocally related an accumulation of ADR is accompanied by a decrease in ATR and the amount of energy available to the celL Therefore, ADR accumulation signals the need for ATR synthesis. ADR aUosterically activates isocitrate dehydrogenase, thereby increasing the rate of the citric acid cycle and the production of NADH and FADH. The elevated levels of these reduced coenzymes, in turn, increase the rate of electron transport and ATR synthesis. 

The overall rate of the citric acid cycle is controlled by the rate of conversion of pyruvate to acetyl-CoA and by the flux through citrate synthase, isocitrate dehydrogenase, and a-lcetoglutarate dehydrogenase. These fluxes are largely determined by the concentrations of substrates and products the end products ATP and NADH are inhibitory, and the substrates NAD+ and ADP are stimulatory. 

The same intermediates of glycolysis and the citric acid cycle that activate isocitrate dehydrogenase are allosteric inhibitors of isocitrate lyase. When energy-yielding metabolism is sufficiently fast to keep the concentrations of glycolytic and citric acid cycle intermediates low, isocitrate dehydrogenase is inactivated, the inhibition of isocitrate lyase is relieved, and isocitrate flows into the glyoxylate pathway, to be used in the biosynthesis of carbohydrates, amino acids, and other cellular components. 

The acid is measured using the enzyme isocitrate dehydrogenase. Isocitrate is present in a small but fairly constant amount. Table IV gives the concentrations and ratios with citric acid. 

To measure the activity of an enzyme of the citric acid cycle, isocitrate dehydrogenase, and the effect of enzyme concentration on the rate of reaction. 

Figure 17.18. Control of the Citric Acid Cycle. The citric acid cycle is regulated primarily by the concentration of ATP and NADH. The key control points are the enzymes isocitrate dehydrogenase and a-ketoglutarate dehydrogenase.

Hemolysis is defined as the disruption of the red cell membrane and results in the release of hemoglobin. Serum shows visual evidence of hemolysis when the hemoglobin concentration exceeds 200 ing/L. Slight hemolysis has little effect on most test values. Severe hemolysis causes a slight dilutional effect on those constituents present at a lower concentration in the erythrocytes than in plasma. However, a notable effect may be observed on those constituents that are present at a higher concentration in erythrocytes other than in plasma. Thus plasma activities or concentrations of aldolase, total acid phosphatase, lactate dehydrogenase, isocitrate dehydro-... 

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