Conversion to acetyl CoA

Oxidation of 2 molecules of glyceraldehyde-3-phosphate yields 2 NADH Pyruvate conversion to acetyl-CoA (mitochondria) 2 NADH Citric acid cycle (mitochondria) 2 molecules of GTP from 2 molecules of succinyl-CoA + 2 + 2... 

When a fatty acid with an even number of carbon atoms is broken down through P oxidation the last intermediate before complete conversion to acetyl-CoA is the four-carbon acetoacetyl-CoA ... 

The methyl group in the (3 position blocks complete (3 oxidation, but an aldol cleavage would be possible to give acetyl-CoA and acetone. However, acetone is not readily metabolized further. By addition of C02 the product becomes acetoacetate, which can readily be completely metabolized through conversion to acetyl-CoA. 

Answer In these individuals, the usual route for pyruvate metabolism—conversion to acetyl-CoA and entry into the citric acid cycle—is slowed by the decreased capacity for carrying electrons from NADH to oxygen. Accumulation of pyruvate in the tissues shifts the equilibrium for pyruvate-alanine transaminase, resulting in elevated concentrations of alanine in tissues and blood. 

D. The increased concentrations of pyruvate, lactate, and alanine indicate that there is a block in the pathway leading from pyruvate toward the TCA cycle. A deficiency in pyruvate dehydrogenase would lead to a buildup of pyruvate. Pyruvate has three fates other than conversion to acetyl-CoA by pyruvate dehydrogenase conversion to oxaloacetate by pyruvate carboxylase, reduction to lactate by lactate dehydrogenase, and transamination to the amino acid alanine. Thus, because pyruvate builds up, an increase in lactate and alanine would be expected if pyruvate dehydrogenase was deficient. 

In tissues other than the RBC, pyruvate has alternative metabolic fates that, depending on the tissue, include gluconeogenesis, conversion to acetyl-CoA by pyruvate dehydrogenase for further metabolism to CO in the tricarboxylic acid (TCA) cycle, transamination to alanine or carboxylation to oxaloacetate by pyruvate carboxylase (Table 23-1). In the RBC, however, the restricted enzymatic endowment precludes all but the conversion to lactate. The pyruvate and lactate produced are end products of RBC glycolysis that are transported out of the RBC to the liver where they can undergo the alternative metabolic conversions described above. 

Activation of ketone bodies. This diagram shows the steps in the activation of ketone bodies and their conversion to acetyl CoA. This occurs in the mitochondria of many types... 

Entry into the TCA cycle and exit as citrate, followed by conversion to acetyl CoA, mal-onyl CoA, and entry into fatty acid synthesis and secretion as VLDL... 

The first step is a decarboxylation of pyruvate and its conversion to acetyl-CoA, with the concommitant production of NADH. The next step is a condensation reaction between acetyl-CoA and oxaloacetate to produce the six-carbon compound, citrate. Citrate is isomerized to isocitrate. 

In 1948, Lipmann and his coworkers established the structure and the role of coenzyme A in its conversion to acetyl CoA (see the structure below), noting that the thioacetate linkage (-S-COCH3) is a high-energy linkage like the pyrophosphate linkage in ATP. The presence of pantothenic acid, one of the B vitamins, in the structure of coenzyme A (see the structure) explains its vital role in intermediary metabolism. For these... 

Acetate is a final product of ethanol oxidation. Its utilization by muscles and brain cells requires its conversion to acetyl-CoA by acetyl-CoA synthase. This consumes ATP, yielding AMP and energy deficits, which in turn stimulate purine nucleotide catabolism and hyperuricemia (Lavoie and Butterworth 1995). Through such mechanisms, alcohol may exert direct toxic elfects uncovering pre-existing subclinical TD-dependent energy shortages. 

CoA is largely followed by a decarboxylation to acetyl-CoA and 3HB synthesis. But a portion of the 3-hydroxypropionyl-CoA is also directly polymerized into 3HP, presumably under the action of PHA synthase, producing a random copolyester of 3HB and 3HP units. When 1, 5-pentanediol or 1, 7-heptanediol are used as carbon sources, formation of 3-hydroxypropionyl-CoA probably results from the P-oxidation of the longer acyl-CoAs derived from the substrates. The authors noted that since R. eutropha can grow on 3-HP acid, conversion to acetyl-CoA is probably the favored step, and only low contents of 3HP (7 mol%) in the polyester are observed with this micro-organism when 3HP acid is the sole carbon source. 

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