354 RIBOFLAVIN 



lyzed the oxidation of the following thirteen natural amino acids to their 

 keto derivatives: leucine, methionine, proline, norleucine, norvaline, phenyl- 

 alanine, tryptophan, isoleucine, tyrosine, valine, histidine, cystine, and 

 alanine. 



The specificities of the L-hydroxy acid oxidase are similar to those of the 

 L-amino acid oxidase ;^^ there is a pronounced relationship between the 

 length of the carbon chain and the rate of oxidation. The turnover number 

 of L-amino oxidase is very low (about 6). 



c. Mechanism of Action 



In the presence of oxygen as hydrogen acceptor, one molecule of oxygen 

 is taken up for each molecule of amino acid oxidized, and one molecule 

 each of keto acid, NH3 , and H2O2 are formed. Methylene blue can replace 

 oxygen as the hydrogen acceptor. 



12. Glycine Oxidase 



Prior to the isolation of glycine oxidase by Ratner et al.,^^ three enzymes 

 were known which could deaminate amino acids oxidatively: D-amino acid 

 oxidase, L-amino acid oxidase, and L-glutamic dehydrogenase. None of 

 these has any activity toward glycine. 



a. Preparation 



Glycine oxidase, which was found in the liver or kidney of all animals 

 tested, was extracted^* from an acetone powder of pig kidneys and precipi- 

 tated with 30 % saturated ammonium sulfate. The precipitate was dissolved 

 in water and precipitated twice in 24% monopotassium acid phosphate. 

 The enzyme preparation retained activity for 7 to 10 days at 0.5°. It was 

 rapidly destroyed (80 % in 12 hours) by dialysis against water. 



b. Properties 



Solutions are pale greenish yellow but water-clear. These can tolerate 

 3 minutes' exposure to 55° without appreciable loss of activity. Flavin 

 adenine dinucleotide is the prosthetic group, and it can be reversibly sepa- 

 rated from the apoenzyme. Glycine oxidase catalyzes the oxidation of 

 glycine and N-monomethylglycine (sarcosine), but not other substituted 

 products or peptides of glycine. 



c. Mechanism of Oxidation 



The oxidation of glycine (where R is H) or sarcosine (where R is CH3) 

 9^ S. Ratner, V. Nocito, and D. E. Green, /. Biol. Chem. 152, 119 (1944). 



