Glycolysis lactate from

Glycolysis A net formation of two results from the formation of lactate from one molecule of glucose, generated in two reactions catalyzed by phospho-glycerate kinase and pyruvate kinase, respectively (Figure 17-2). 

When animal tissues cannot be supplied with sufficient oxygen to support aerobic oxidation of the pyruvate and NADH produced in glycolysis, NAD+ is regenerated from NADH by the reduction of pyruvate to lactate. As mentioned earlier, some tissues and cell types (such as erythrocytes, which have no mitochondria and thus cannot oxidize pyruvate to C02) produce lactate from glucose even under aerobic conditions. The reduction of pyruvate is catalyzed by lactate dehydrogenase, which forms the l isomer of lactate at pH 7 ... 

The use of alanine to transport ammonia from skeletal muscles to the liver is another example of the intrinsic economy of living organisms. Vigorously contracting skeletal muscles operate anaerobically, producing pyruvate and lactate from glycolysis as well as... 

The beauty of the metabolic cycle through pyruvate, shown in summary in Figure 20-11, is the way it can be tapped at various points according to whether the organism requires ATP (from glycolysis), NADH (from pentose shunt), or NAD (from the lactate siding). 

When complex I is defective, there is an excess of cellular NADH, which pushes the lactate dehydrogenase to form lactate from pyruvate (anaerobic glycolysis). This results in higher than normal utilization of glucose, causing hypoglycemia. Because succinate is oxidized at the complex II level, its oxidation is not affected. 

Inhibitors determined for the controlling enzymes involved in cell chemistry have been listed elsewhere (Hoffman, 1999, Table A-1 through Table A-3 of Appendix A), as obtained from Jain s Handbook of Enzyme Inhibitors (1982) and Zollner s Handbook of Enzyme Inhibitors (1993). The breakdown is for glycolysis, lactate formation, and glutaminolysis. Some of the more common and simpler chemicals or compounds serving as enzyme inhibitors for one or another of the various reactiou steps are as follows, as derived from the Jain and Zollner references. Many more, natural or synthetic, no doubt remain to be discovered, as both the Jain and Zollner references are dated. The sequences presented here parallel those presented by Hoffman (1999). 

In anaerobic glycolysis, electrons from NADH do not enter the electron transport chain (see here). Anaerobic glycolysis pathways include lactate fermentation and ethanol fermentation. 

The sprint is essentially anaerobic and produces lactate from glucose by glycolysis. Lactate is then recycled to glucose by gluconeogenesis. 

The Cori cycle is a pathway in which there is cycling of glucose due to glycolysis in muscle and gluconeogenesis in liver. The blood transports lactate from muscle to liver and glucose from liver to muscle. 

Fig. 1 0.3 A simple model of the reaction mechanism of glycolysis. For definition of symbols see fig. 6.1. FDP, fructose diphosphate PYR, pyruvate LAC, lactate. (From [11].)...

The following O2-linked metaboHtes have been implicated as potential chemical mediators in the metabolic hypothesis adenosine (from ATP hydrolysis ATP ADP —> AMP — adenosine), H+, and lactate (from lactic acid generated by glycolysis). Their levels are increased when there is a reduction in O2 supply relative to demand (i.e., tissue hypoxia). The production of more CO2 as a result of increased tissue activity (leading to increased oxidative metabolism) leads to vasodilation through increased H+ concentration. Increased potassium ion and interstitial fluid osmolarity (i.e., more osmoticaUy active particles) transiently cause vasodilation under physiological conditions associated with increased tissue activity. 

The removal of lactate from muscle cells shifts the equilibrium to the right, ensuring the regeneration of NAD and the production of pyruvate by glycolysis. In the hver, pyruvate is used to make glucose, thus decreasing the pyruvate concentration, which shifts the equihbrium to the left and prevents the accumulation of lactate. 

Heavy exercise would cause anaerobic conditions to occur in some cells, which would then release lactate from glycolysis into the bloodstream. 

Glycolysis takes place in the cell cytoplasm, whereas the decarboxylation of pyruvate and the subsequent oxidation of acetyl-coenzyme A via the tricarboxylic acid cycle take place in the mitochondrial matrix. Under anaerobic conditions, oxygen is not available for the oxidation of reduced NAD by oxidative phosphorylation, in order to allow the release of a small amount of energy by continuing the breakdown of glucose to pyruvate, reduced NAD must be converted to the oxidised form, if not, step 7 of Fig. 9.4 will not take place and energy production will be blocked. Oxidation of reduced NAD may be achieved under such conditions by the formation of lactate from pyruvate in the presence of lactate dehydrogenase ... 

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