Amino acid pyruvate from

In solutions of histidine and histamine containing pyruvic acid, another reaction takes place (9) in addition to the formation of Schiff base. With increasing concentration of these amino acids apart from the formation of the wave of the Schiff base at a more positive potential, a decrease of the total limiting current can be observed (Fig. 5). The decrease corresponds to the formation of a polarographically inactive compound this may be interpreted by reaction (6) ... 

It is of interest to compare the tertiary structure of AspAT with that of other PLP-dependent enzymes. Some PLP enzymes whose primary structures are quite different from AspAT exhibit similar tertiary structures. Such enzymes are a>-amino acid pyruvate aminotransferase,341 phosphoserine aminotransferase351 and tyrosine-phenol lyase361 (Phillips, R., personal communication). Similarity in tertiary structure among these PLP enzymes may lead to the idea that many PLP-dependent enzymes share the same ancestor protein. There are PLP enzymes belonging to its own category, such as glycogen phosphorylase and tryptophan synthase.37 381 These enzymes do not share any similarities in either primary or tertiary structures with AspAT. 

The nonessential amino acids are synthesized by quite simple reactions, whereas the pathways for the formation of the essential amino acids are quite complex. For example, the nonessential amino acids alanine and aspartate are synthesized in a single step from pyruvate and oxaloacetate, respectively. In contrast, the pathways for the essential amino acids require from 5 to 16 steps (Figure 24.8). The sole exception to this pattern is arginine, inasmuch as the synthesis of this nonessential amino acid de novo requires 10 steps. Typically, though, it is made in only 3 steps from ornithine as part of the urea cycle. Tyrosine, classified as a nonessential amino acid because it can be synthesized in 1 step from phenylalanine, requires 10 steps to be synthesized from scratch and is essential if phenylalanine is not abundant. We begin with the biosynthesis of nonessential amino acids. 

We ll see in Chapter 29 that living organisms use many of the same tions that chemists use in the laboratory. This is particularly true of i bonyl-group reactions, where nucleophilic addition steps play a critical ruie in the biological synthesis of many vital molecules. For example, one of the pathways by which amino acids are made involves nucleophilic addition of an amine to w-keto acids. To choo.se a specific example, the bacterium Bari/ lus subtilis synthesizes the amino acid alanine from pyruvic acid. 

Figure 23.23 Pyt uvate formation from amino acids. Pyruvate is the point of entry for alanine, serine, cysteine, glycine, threonine, and tryptophan.

Outline the biosynthesis of the amino acid glutamate from pyruvate. 

The amino acids differ from other classes of biomolecules in that each member of this class is synthesized by a unique pathway. Despite the tremendous diversity of amino acid synthetic pathways, they have one common feature. The carbon skeleton of each amino acid is derived from commonly available metabolic intermediates. Thus in animals, all NAA molecules are derivatives of either glyc-erate-3-phosphate, pyruvate, a-ketoglutarate, or oxaloacetate. Tyrosine, synthesized from the essential amino acid phenylalanine, is an exception to this rule. 

Decarboxylases enzymes which catalyse removal of a carboxyl group as COj (see Decarboxylation) from a-ketoacids or from amino acids. Pyruvate decarboxylase (see) is an important enzyme of carbohydrate metabolism. For amino acid D., see Pyridoxal phosphate. 

The major pathway of serine catabolism probably is by way of its enzymatic dehydration and subsequent spontaneous deamination to yield pyruvic acid (see Fig. 2). An evidence for this is the observation of Lien and Greenberg that alanine is the major amino acid formed from serine-3-C by liver mitochondrial preparations. The alanine could be fomed from the pyruvic acid by transamination. 

The carbon skeleton of amino acids originates from glycolysis intermediary products (pyruvate, 3-phosphoglycerate, phosphoenolpyruvate), the... 

P. (2011) Accumulation of amino acids deriving from pyruvate in Escherichia coli W3110 during fed-batch cultivation in a two-compartment scale-down bioreactor. Adv. Biosci. Biotechnol, 2 (5), 336-339. 

Return of the amino acid back from the pyruvate by amino acid dehydrogenase... 

The amino acids derived from pyruvate or 3-phosphogIycerate include alanine, serine, and glycine. Synthesis of these amino acids can be achieved by multiple pathways involving several different subcellular compartments. Although enzymes that could contribute to their biosynthesis are easily demonstrable in plants (Miflin and Lea, 1982), the relative contribution of each potential pathway may vary from species to species, and within a single organism in different tissues or under different physiological conditions. 

Figure 4.5 The polypeptide chain of the enzyme pyruvate kinase folds into several domains, one of which is an a/p barrel (red). One of the loop regions in this barrel domain is extended and comprises about 100 amino acid residues that fold into a separate domain (blue) built up from antiparallel P strands. The C-terminal region of about 140 residues forms a third domain (green), which is an open twisted a/p structure.

L-Glutamic acid is not an essential anino acid. It need not be present in the diet because animals can biosynthesize it from sources of a-ketoglutaiic acid. It is, however, a key intennediate in the biosynthesis of other amino acids by a process known as transamination. L-Alanine, for example, is fonned from pyruvic acid by transamination from L-glutamic acid. 

A rather limited collection of simple precursor molecules is sufficient to provide for the biosynthesis of virtually any cellular constituent, be it protein, nucleic acid, lipid, or polysaccharide. All of these substances are constructed from appropriate building blocks via the pathways of anabolism. In turn, the building blocks (amino acids, nucleotides, sugars, and fatty acids) can be generated from metabolites in the cell. For example, amino acids can be formed by amination of the corresponding a-keto acid carbon skeletons, and pyruvate can be converted to hexoses for polysaccharide biosynthesis. 

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