AMINO-ACID CATABOLISM U 



the D stereo-isomers of their substrates, 



RCH(NH,)COOH+H20=RCOCOOH+NH3+2H 



The transfer of hydrogen from the amino-acid to a suitable 

 acceptor, typically Og , appears to be mediated by one or 

 more carrier substances, and usually the enzyme has a 

 prosthetic group capable of functioning in this manner. 

 Enzymes of this type are the L-amino-acid oxidases of 

 Neurospora crassa and N. sitophila [7], Proteus vulgaris [58], 

 Penicillium notatum and Aspergillus niger [37]. Each of these 

 oxidases attacks a wide variety of amino-acids, although the 

 possibility that the observed activity is due to several very 

 similar, but specific, enzymes has not been ruled out. 

 Oxygen can be replaced in vitro by reducible dyes, such 

 as methylene blue, or by ferricyanide. There is evidence 

 that the enzyme from N. crassa possesses a prosthetic 

 group, adenine flavindinucleotide, which enables hydrogen 

 to be transferred directly to Og , resulting in the formation 

 of H2O2 [10]. In the presence of catalase (present in Neuro- 

 spora), the oxidation of one gram mole of amino-acid 

 involves the overall uptake of one gram atom of oxygen. The 

 mycelium of N. crassa also contains a similar oxidase 

 specific for D-amino-acids [7]. 



Whether the oxidase from Pr. vulgaris also has a flavin 

 prosthetic group has not yet been established, and although 

 one atom of oxygen is taken up per molecule of amino-acid 

 oxidized, there is no evidence that HgOg is first formed and 

 subsequently decomposed by catalase. There must be more 

 than one oxidase in Pr. vulgaris since washed suspensions 

 oxidize more amino-acids than the cell-free enzyme pre- 

 paration [58]. Oxygen is required for the deamination 

 of glycine, alanine and glutamic acid by washed cell sus- 

 pensions of Escherichia coli, Pseudomonas fluorescens and 

 Bacillus mycoides [cf. 25]: using cells treated with toluene to 

 prevent the further metabolism of pyruvate, it can be shown 

 that the deamination of alanine by Esch. coli proceeds 

 quantitatively according to the following equation: 



CH3CH(NH2)COOH+i02=CH3COCOOH+NH3 



