Intracellular Krebs Cycle

Since the intracellular ratios of NADH/NAD+, NADPH/NADP+, and ATP/ adenylates are carefully regulated by the cell, loss of the reduced nucleotide can be compensated by faster operation of the Krebs cycle. But the cell can only make up for a net loss of all nucleotides by an increase in synthesis. The oxidation of NADPH or NADH results in elevated enzyme activity, and this permits the cell to restore the initial ratio of the nucleotides. With NADPH, its oxidation increases the activity of the pentose phosphate pathway. Such increase also occurs following the oxidation of GSH as shown below. Oxidation of either NADPH or GSH, therefore, may be responsible for the apparent increase in the enzymes found in the pentose phosphate pathway after repeated 03 exposure. 

Finally, perhaps an explanation for the beneficial effects of coenzyme A (CoA), malate and pyruvate for the extracellular in vitro growth of P. lophurae found by Trager (1952) and interpreted by Moulder (1962) to neatly explain the shift in pattern of carbohydrate metabolism accompanying liberation of parasites from the host cell. .. (The) lack of CoA in free parasites logically explains the lessened rate of pyruvic acid oxidation via the Krebs cycle. It is difficult to escape the conclusion that the inability of plasmodia to synthesize CoA extracellularly results in extensive dislocations in glucose metabolism, which in turn contribute heavily to the restriction of the malarial parasite to an intracellular habitat is this malate and pyruvate could be linked to the generation of dihydronicotinamide adenine dinucleotide (NADH) for glycolysis, and a CoA deficiency could limit activity in pathways other than the TCA cycle. 

The relationship between the enzymes of the Krebs cycle and cellular structure is surely one of the most challenging chapters in cellular biochemistry. For years investigators sought to determine two things the intracellular distribution of the enzymes of the Krebs cycle, and the relationship between enzymes and the mitochondrial structures. We shall now review these two lines of investigation [80]. 

Rice bran is the richest natural source of B-complex vitamins. Considerable amounts of thiamin (Bl), riboflavin (B2), niacin (B3), pantothenic acid (B5) and pyridoxin (B6) are available in rice bran (Table 17.1). Thiamin (Bl) is central to carbohydrate metabolism and kreb s cycle function. Niacin (B3) also plays a key role in carbohydrate metabolism for the synthesis of GTF (Glucose Tolerance Factor). As a pre-cursor to NAD (nicotinamide adenine dinucleotide-oxidized form), it is an important metabolite concerned with intracellular energy production. It prevents the depletion of NAD in the pancreatic beta cells. It also promotes healthy cholesterol levels not only by decreasing LDL-C but also by improving HDL-C. It is the safest nutritional approach to normalizing cholesterol levels. Pyridoxine (B6) helps to regulate blood glucose levels, prevents peripheral neuropathy in diabetics and improves the immune function. 

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