Biochemistry of Amino Acids - A. Meister 1961

General Biochemistry and Physiology of Amino Acid Metabolism
Oxidative Deamination
L-Amino Acid Oxidase

Only a single L-amino acid oxidase preparation has been obtained from mammalian Tissues; it was isolated from rat Kidney by Blanchard and coworkers [118]. This enzyme, which catalyzes The oxidation of 13 L-Amino Acids (see Table 18), was purified and found to have a turnover number of approximately 6. It differs from other general amino acid oxidases in that its coenzyme is riboflavin phosphate. A notable property of this enzyme is that it oxidizes L-α-hydroxy acids somewhat faster than L-amino acids. The substrate Specificity of the enzyme toward amino acids is similar to that of D-Amino Acid Oxidase; both Enzymes are characterized by very slow oxidation of dicarboxylic and diamino acids. Aside from the kidney, L-amino acid oxidase has not been found in other animal tissues. It seems unlikely that an enzyme so sparsely distributed and possessing such low activity could play a significant role in the general deamination of L-amino acids in mammals.

Zeller and coworkers [145–147] discovered L-amino acid oxidase (snake venom amino acid oxidase) in the venoms and tissues of many snakes. The activity of many dried snake venoms is very high; Zeller found that the venom of Vipera aspis exhibits the highest activity. In purified form, the enzyme was isolated from the venom of the cottonmouth moccasin; its coenzyme was established to be flavin adenine dinucleotide [119]. The substrate specificity of snake L-amino acid oxidase is shown in Table 18; species differences are noted in the relative rates of oxidation of individual amino acids, although the GENERAL PATTERNS OF substrate specificity are similar among different species. Like the kidney D-amino acid oxidase, this enzyme oxidizes Lysine and Ornithine very slowly, whereas the ω-N-acyl derivatives of these Amino acids are oxidized quite rapidly. Similarly, glutamine and asparagine, unlike the corresponding dicarboxylic acids, are oxidized relatively quickly by snake L-amino acid oxidase. In contrast to D-amino acid oxidase, L-amino acid oxidase does not oxidize Proline, hydroxyproline, or N-monomethyl amino acids. L-Isoleucine and L-allo-isoleucine are oxidized by it to the L- and D-forms of α-keto-β-methylvaleric acid without racemization during the oxidation process. It was found that the L-stereoisomers of β-phenylserine are oxidized by snake L-amino acid oxidase in the absence of catalase to the corresponding optically active mandelic acids [148]. The enzymatic oxidation of the four isomers of isoleucine and the two L-stereoisomers of β-phenylserine to optically active products further confirms that the β-hydrogen atom is not involved in the oxidation process (see p. 189).

Interesting studies concerning the oxidation of the isomers of α,ε-diaminopimelic acid and some of its derivatives were conducted by Work [149]. The L-amino acid oxidase of the mold Neurospora oxidizes LL-diaminopimelic acid as actively as the meso-form and the D-monoamide of L-diaminopimelic acid. The oxidation of these substrates proceeds at approximately the same rate as the oxidation of L-Methionine and L-lysine.

Unlike the oxidation of the LL-form, which consumes two atoms of oxygen (in the presence of catalase), the oxidation of the meso-form consumes only one oxygen atom.

The physiological significance of snake L-amino acid oxidase remains unclear. The toxicity of snake venom does not appear to be related to the presence of this enzyme.

Active L-amino acid oxidases have been found in many microorganisms, including Neurospora crassa, in which The formation of this enzyme is stimulated by biotin [150]. It is possible that biotin does not exert a direct effect on enzyme synthesis, since this vitamin is required for the growth of the mold itself.

Class="center">

Interestingly, some species of N. crassa produce both D- and L-amino acid oxidases simultaneously, whereas other species produce only a single oxidase with D- or L-specific action [131, 150, 151]. L-Amino Acid oxidases have been found in A number of Penicillium strains, Aspergillus niger, Proteus, and Aerobacter aerogenes [124, 131, 150, 152, 153]. The enzyme from Proteus vulgaris [153] has been obtained in a purified state, and its substrate specificity has been studied (see Table 18). An L-amino acid oxidase acting on diamino acids has been found in turkey Liver (see p. 343).