Pyruvate formation from

Figure 23.22. Pyruvate Formation from Amino Acids. Pymvate is the point of entry for alanine, serine, cysteine, glycine, threonine, and tryptophan.

Various methods of pyruvate formation from (i )-lactate. The procedures are applicable to other (/ )-2-hydroxy carboxylates, too (62). 

The fonn in which acetate is used in most of its important biochemical reactions is acetyl coenzyme A (Figure 26.1a). Acetyl coenzyme A is a thioester (Section 20.13). Its formation from pyruvate involves several steps and is summarized in the overall equation ... 

Citraconic anhydride formation from pyruvic acid by oxidative decarboxy-condensation has not been known prior to these studies. Therefore, in this paper, we attempted to get more insight into the new reaction. 

Bakken, I. J., White, L. R., Aasly, J. etal. Lactate formation from [U-13C] aspartate in cultured astrocytes compartmentation of pyruvate metabolism. Neurosci. Lett. 237 117-120, 1997. 

In the weU-fed, absorptive state (insulin), accumulating acetyl CoA is shuttled into the cytoplasm for fatty acid synthesis. OAA is necessary for this transport, and acetyl CoA can stimulate its formation from pyruvate (see Chapter 15, Figure 1-15-1). 

It may be stated at this point that the presence of a /3-hydroxy-butyrate fat in certain organisms is a matter of general biochemical importance. Usually /3-hydroxybutyric acid and the acetone bodies are derived from n-butyric acid directly. The unambiguous formation of jS-hydroxybutyric acid anhydrides from carbohydrates opens up new vistas its formation from acetaldehyde, and from pyruvic acid, through aldol intermediates can be understood without difficulty. Kirrmann s reaction, to which little attention has been paid, is at the same time an example of an oxygen shift, leading from hydroxyaldehydes to fatty acids. 

The actual formation of pyruvic acid from various mercapturic acids upon which these formulae for cysteine and cystine were founded, was only shown later by Baumann s pupils, Konigs, Brenzinger and Schmitz, and in conjunction with Suter s observation that a-thiolactic acid was formed by the hydrolysis of horn, this formula for cystine was accepted. The results obtained, however, scarcely justified this formula as pointed out by Friedmann in 1902, who showed conclusively that the cystine, obtained from proteins, had not this constitution. 

Hayami and his coworkers have studied the mechanism of formation of acetol and pyruvic acid from D-glucose- -14C, -6-14C, and -3,4-14C2, reacting in a concentrated, phosphate buffer solution.148-151 Their data supported the supposition that the products are formed from pyruvaldehyde by way of a Cannizarro reaction. As in the formation of lactic acid, the pyruvaldehyde can be formed either from the reducing or the nonreducing end of the D-glucose molecule, and the distribution of radioactivity in the pyruvic acid and acetol... 

When grown in alkaline media, certain species of lactic acid bacteria decrease production of LDH, resulting in increased formation of formate, acetate, and ethanol as end products. This phenomenon has been observed in S. faecalis subsp. liquefaciens (Gunsalus and Niven 1942), Streptococcus durans, S. thermophilus, (Platt and Foster 1958), and Lactobacillus bulgaricus (Rhee and Pack 1980). Data of Rhee and Pack (1980) indicate that a phosphoroclastic split of pyruvate occurs under alkaline conditions to yield ATP. The enzymes involved in this reaction (pyruvate formate-lyase and acetate kinase) require alkaline conditions for optimum activity. A shift from homo- to heterofermentation because of increased pH has not been observed for Group N streptococci. 

Of the six moles of ATP generated from 1.5 moles of glucose, three are derived from formation of pyruvate, one from formation of acetate from acetyl phosphate, and two from reduction of fumerate to succinate. 

The activating enzyme will also generate radicals from short peptides such as Arg-Val-Ser-Gly-Tyr-Ala-Val, which corresponds to residues 731-737 of the pyruvate formate-lyase active site. If Gly 734 is replaced by L-alanine, no radical is formed, but radical is formed if D-alanine is in this position. This suggests that the pro-S proton of Gly 734 is removed by the activating... 

This compound undergoes a two-step ATP-dependent cyclization352-355 to form dethiobiotin. The final step, insertion of sulfur into dethiobiotin, is catalyzed by biotin synthase, a free-radical-dependent enzyme related to pyruvate formate lyase (Fig. 15-16). It transfers the sulfur from cysteine via an Fe-S cluster.3553 Biosynthesis of lipoic acid involves a similar insertion of two sulfur atoms into octanoic acid.356 See also p. 1410. 

The a-keto acid decarboxylases such as pyruvate (E.C. 4.1.1.1) and benzoyl formate (E.C. 4.1.1.7) decarboxylases are a thiamine pyrophosphate (TPP)-dependent group of enzymes, which in addition to nonoxidatively decarboxylating their substrates, catalyze a carboligation reaction forming a C-C bond leading to the formation of a-hydroxy ketones.269-270 The hydroxy ketone (R)-phenylacetylcarbinol (55), a precursor to L-ephedrine (56), has been synthesized with pyruvate decarboxylase (Scheme 19.35). BASF scientists have made mutations in the pyruvate decarboxylase from Zymomonas mobilis to make the enzyme more resistant than the wild-type enzyme to inactivation by acetaldehyde for the preparation of chiral phenylacetylcarbinols.271... 

So far, two types of aminomutase have been investigated in detail. Lysine 2,3-aminomutase from Clostridium subterminale SB4 is the example par excellence for the SAM-dependent type of aminomutase. Several other enzymes belonging to the same family are known. Examples are biotin synthase [82], pyruvate formate lyase [83, 84], and anaerobic ribonucleotide reductase [85]. 

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