148 THE BIOCHEMISTRY OF B VITAMINS 



strates are not the naturally occurring isomers. Only the dinucleotide can 

 function as the prosthetic group of this flavoprotein. 



L-amino oxidase 68 (L-hydroxy acid oxidase) is an interesting and 

 unusual enzyme in that it will not only catalyze the oxidation of at least 

 thirteen amino acids but will also bring about comparable dehydrogena- 

 tion of L-a-hydroxy acids having structures related to the a-amino acids. 69 

 Its coenzyme is riboflavin monophosphate. 70 The enzyme was isolated 

 from rat kidney. It has been shown that certain bacteria possess a similar 

 enzyme, some properties of which differ from the animal preparations. 71 

 Molds are the source for a third preparation, the activity of which differs 

 in minor respects from both the mammalian and bacterial enzymes. 72 

 One of the active principles in snake venom is an L-amino acid oxidase, 

 and although its relation to the other oxidases just mentioned has not 

 been ascertained, it is believed to be a flavoprotein. 73 



Glycine is oxidized by neither of these types of enzymes, but is attacked 

 by a specific enzyme, glycine oxidase. 74 The cofactor is flavin adenine 

 dinucleotide. 



Aldehyde oxidases. It has been shown that there are three flavo- 

 proteins capable of catalyzing the oxidation of aldehydes. It is believed 

 that each enzyme of this group contains adenine dinucleotide as its pros- 

 thetic group. Milk was the first substance to be used as a source of an 

 "aldehyde oxidizing" flavoprotein, an enzyme which catalyzes the de- 

 hydrogenation of formaldehyde hydrate and other aliphatic and aromatic 

 aldehydes. 75 Strangely enough, this enzyme, or another flavoprotein which 

 cannot be separated from it, was later found to catalyze the oxidation 

 of hypoxanthine and xanthine. 76 A second aldehyde oxidase was isolated 

 from plant tissues, 77 but this enzyme was incapable of oxidizing purines. 

 That it is likewise a flavoprotein has never been demonstrated. Liver has 

 been found to contain an aldehyde oxidase which differs from liver 

 xanthine oxidase. 78 Penicillium notatum produces a flavoprotein which 

 was prematurely classified as an antibiotic, notatinP Further investiga- 

 tion showed this flavoprotein to be a glucose oxidase. The bactericidal 

 effect of this enzyme is observed only in the presence of glucose and 

 oxygen in which case hydrogen peroxide accumulates, killing bacteria 

 which do not contain peroxidases. 80 It has been shown that xanthine 

 oxidase can be made to demonstrate similar action against certain 

 bacteria. 81 



Xanthine oxidase. Xanthine oxidase catalyzes the oxidation of hypo- 

 xanthine and xanthine to uric acid by removing two hydrogen atoms 

 from the hydrated purine base. 



Milk serves as an especially good source of this enzyme, although it is 

 found widely distributed in animal tissues. Highly purified preparations 



