FUNCTION 



flavine-adenine-dinucleotide, it was inactive towards all the substrates 

 tried ; it contained o-86 % of flavine phosphate. 



A. E. Axelrod and C. A. Elvehjem ^^ found that the xanthine oxidase 

 content of rat liver was markedly reduced in rats fed a riboflavine- 

 deficient diet ; addition of the prosthetic group to the liver homogenate 

 failed to increase the activity, so that the reduction in activity would 

 appear to be due to a deficiency of the protein part of the enzyme. 

 Addition of riboflavine to the diet, however, resulted in rapid restora- 

 tion of the liver xanthine oxidase to normal. 



D-Amino Acid Oxidase 



The oxidation of amino acids to keto acids via imino acids is also 

 brought about by an enzjone containing ribofiavine-adenine-dinucleo- 

 tide,3^-3® and Axelrod et al.^^ showed that a deficiency of riboflavine 

 in the diet of rats reduced the D-amino acid oxidase content of liver 

 and kidney ; administration of riboflavine restored the enzyme activity 

 to normal. 



This observation presumabl}?" explains why rats on a diet providing 

 less than 2-5 /zg. of riboflavine per day did not utilise protein as effi- 

 ciently as rats fed 5 /xg. or more per day.*^** 



Krahl et al.^^ claimed that the oxidation of a-alanine by D-amino 

 acid oxidase was inhibited by certain phenols • containing nitro or 

 halogen groups, e.g. dinitrophenol, at relatively high concentrations, 

 but Haas et al^^ showed that the pyridine-catalysed dehydrogenation 

 of hexose-6-phosphate was even more strongly inhibited than the 

 flavine enzyme. 



Hoagland et al.^^ obtained a fla vine-containing compound from the 

 elementary bodies of vaccinia, 100 g. of virus containing i-i to 1-5 

 mg. of riboflavine. The substance functioned as a coenzyme for 

 D-amino acid oxidase, and was probably a flavine adenine dinucleotide. 



The specificity of D-amino acid oxidase has been the subject of 

 controversy, but most workers agree that D-glutamic acid and D -lysine 

 are not attacked by the isolated enzyme system. Handler et al.^^ 

 found that the N-methyl derivatives of DL-methionine, DL-alanine 

 and DL-leucine were oxidised by D-amino acid oxidase preparations. 

 J. R. Klein and H. Kamin ** found that the enzyme was inhibited by 

 benzoic acid. 



The D-amino acid oxidase of Neurospora ^^ deaminated some nine- 

 teen D-amino acids with optimal activity at pK 8 -o to 8-5. Unlike the 

 enzyme from animal tissues, it is not inhibited by benzoic acid. 



A. Neuberger and F. Sanger *^ found that, although D-lysine was 

 not deaminated by the enzyme, e-acetyl- and e-benzoyl-lysine were 

 oxidised at a moderate rate ; 6-methyl lysine, however, was not 



195 



