Carbohydrates oxidation rates

The first suggestion that substrates in carbohydrate oxidation might exert catalytic effects on the oxidation of other intermediates (cf.earlier demonstration of such action in the urea cycle by Krebs and Henseleit, 1932 see Chapter 6) arose from the work of Szent-Gyorgi (1936). He demonstrated that succinate and its 4C oxidation products catalytically stimulated the rate of respiration by muscle tissues. He also observed that reactions between the 4C intermediates were reversible and that if muscle was incubated with oxaloacetate, fumarate and malate made up 50-75% of the products, 2-oxoglutarate 10-25% and, significantly, 1-2% of the C was converted to citrate. These observations were... 

In a placebo-controlled study in six patients with type 2 diabetes mellitus thalidomide 150 mg/day for 3 weeks reduced insulin-stimulated glucose uptake by 31% and glycogen synthesis by 48% (1115). However, it had no effect on rates of glycolysis, carbohydrate oxidation, non-oxidative glycolysis, lipolysis, free fatty acid oxidation, or re-esterification. The authors concluded that thalidomide increases insulin resistance in obese patients with type 2 diabetes. 

For a given physiologic environment, the heart selects the most efficient substrate for energy production. A fitting example is the switch from fatty acid to carbohydrate oxidation with an acute work jump or increase in workload.15 The transient increase in rates of glycogen oxidation is followed by a sustained increase in rates of glucose and lactate oxidation (Fig. 2). Because oleate oxidation remains unaffected by the work jump, the increase in 02 consumption and cardiac work are entirely accounted for by the increase in carbohydrate oxidation. 

The liver is responsible for synthesis of cholesterol, high-density lipoproteins, and very-low-density lipoproteins. The enzymes lipoprotein lipase and lecithin-cholesterol acyltransferase also are synthesized in this organ. Increased serum triglyceride and FFA concentrations are encountered in patients with hepatic failure, primarily due to the increased lipolysis. The significant insulin resistance that can be seen in cirrhosis causes a shift to lipids as a fuel source. Whereas only 35% of total calories are derived from fat in normal patients after an overnight fast, this can increase to 75% in patients with cirrhosis. Incorporation of late evening snacks in patients with liver cirrhosis may correct abnormal substrate metabolism, increase carbohydrate, and decrease fat oxidation rates. ... 

To investigate the importance, not only of laccase mediators, but also of lacca-ses per se, several laccases were studied for the oxidation of the nonphenolic lignin dimer I. In the presence of the redox mediators 1-HBT or violuric acid, it was found that the oxidation rates of dimer I by the laccases differed considerably. In oxidation of dimer I, both 1-HBT and violuric acid were to some extent, consumed. The consumption rate followed the same order of laccases as the oxidation rates of dimer I. The oxidation rate of dimer I was found to be dependent on both k, jt and the stability of the laccase in question. Both 1-HBT and violuric acid inactivated the laccases— violuric acid to a greater extent then 1-HBT. The presence of dimer I in the reaction mixture slowed down this inactivation. Inactivation seems to be mainly due to the reaction of the redox mediator free-radical with the laccases. No relationship between the carbohydrate content of the laccases and their inactivation was found. When the redox potential of the laccases is in the range of 750-800 mV, i.e., about that of the redox mediator, a further increase in redox potential does not affect k(,jt and the oxidation rate of dimer I [147]. 

Carbohydrates do not absorb in the UV-visible range, but a photo-degradation step is able to reveal their presence in an aqueous solution [20], Contrary to the previous case where the association of UV irradiation with a chemical oxidant (peroxodisulphate) has demonstrated its efficiency, this procedure is not adapted for carbohydrate determination. The oxidation rate of this method is too fast, and absorbing intermediates (carbonyl compounds) are only weakly observed, because they are quickly oxidised into carboxylic acids. Thus, milder oxidation conditions (such as a simple UV lamp) should be used in order to provide an appropriate oxidation reaction that allows the formation of an intermediate compound with a stable absorption peak (Fig. 72). 

In evaluating the reciprocal influence of carbohydrate oxidation and amino acid metabolism it must be borne in mind that the individual metabolic functions of PU, OA or KG, and of AL, AS or GL, are quite different and specific. Their rapid mutual replacement in transaminations will not only affect the rates of metabolic processes, but also qualitatively alter their direction. 

The release and the oxidation processes of the encapsulated D-limonene are closely related to the structural changes in the capsule matrices. Physico-chemical changes caused by the phase transition of carbohydrate from amorphous glass to rubbery are commonly expressed with the temperature difference between the storage temperature, T, and the glass transition temperature, Tg, of the carrier matrices, T — Tg. The idea is based on the fact that the viscosity (or relaxation time) of the carrier matrices follows the Wflliams-Landel-Ferry (WLF) equation expressed as a function of T — Tg (Williams et al., 1955). Therefore, the release rate constants k and the oxidation rate... 

The same method could also be applied to the net substrate oxidation rates. Due to the - at least partial - mutual exchangeability of the substrates as source of energy, this approach was not fully functional for the substrates. In [29] a diet containing 37 % of protein, 4 % of fat and 51 % of CHO (The remainder consists of dietary fiber, water, minerals, etc.) was used. In this case by increasing the protein intake by 1 g the CHO intake was automatically increased by 1.4 g. And in energy metabolism CHO is preferred, as long as there is enough CHO from both intake and body stores available. So the relation of the substrates as fuel differed at different levels of diet intake. This resulted in a fat utilisation factor of up to 800 % and CHO utilisation factors of as low as 33 %. The CD s, however, remained at levels of 92 - 99 %. Only for carbohydrate and... 

The methods of oxidant consumption are used exclusively in the analysis of residual lignin in unbleached pulps. These procedures are all based on the common principle that lignin consumes the appHed oxidants at a much faster rate than the carbohydrates, and oxidant consumption under carefully specified conditions can be regarded as a measure of lignin concentration in the pulp. 

Sophorolipid is a glycolipid, ie it is composed of carbohydrate and lipid. It therefore contains moieties of widely different oxidation levels and its synthesis from single demand carbon sources has a high ATP demand. However, the demand for ATP is reduced if a mixture of glucose and C-18 alkane is used. If glucose and fatty add is used the ATP demand is reduced further and relatively high spedfic production rates can be achieved. 

A few rate coefficients for oxidation by lead tetraacetate have been reported. These, together with those for some carbohydrates, are referred to in the section on glycols (p. 349). 

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