Biochemistry - The Chemical Reactions of Living Cells, Volume 3 - D. Metzler 1980

Metabolism of Nitrogen-Containing Compounds
Alanine and Branched-Chain Amino Acids

As shown in Fig. 14-10, Pyruvate serves as the Starting Material for The Biosynthesis of both L- and D-Alanine, as well as the branched-chain Amino Acids valine, leucine, and isoleucine. The chemistry of these reactions has been discussed in the sections indicated in Fig. 14-10. In Neurospora, isoleucine and valine are synthesized within the Cell/35.html">Mitochondria. Evidence suggests that five Enzymes operating as a multienzyme complex catalyze the synthesis of valine from pyruvate and of isoleucine from pyruvate and Threonine [64]. Another pathway [65], also illustrated in this figure, leads to The formation of pantoic acid, pantetheine, and coenzyme A. Because animals lack the initial enzymes of this pathway, pantothenic acid is an essential vitamin for them. Alanine also acts as a precursor of the vitamin biotin via the Condensation of alanine with a seven-carbon dicarboxylic acid moiety derived from pimeloyl-CoA; this reaction is analogous to the one described by equation (8-20) [65a, b].

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FIG. 14-11. Catabolism of valine, leucine, and isoleucine.