RIBOFLAVINE 



attacked. They suggested that the free basic group in the c-position 

 might inhibit the enzyme by repelUng another basic group in the 

 oxidising enzyme. 



The activity of D-amino acid oxidase was inhibited by mepacrine.*'' 

 The oxidation of glucose, lactate, pyruvate, malate and citrate by rat 

 tissues was also inhibited by the drug, whilst E. Haas *^ found that it 

 also inhibited cytochrome reductase, glucose-6-phosphate dehydro- 

 genase and, to a slight extent, cytochrome oxidase. The addition of 

 I fig. of ribofiavine phosphate counteracted the inhibition of cyto- 

 chrome reductase by 500 fxg. of mepacrine. 



L- Amino Acid Oxidase. 



An enzyme that oxidised L-amino acids was isolated from rat 

 kidney and shown to be a flavo protein.*^ 



Glycine Oxidase 



Glycine oxidase is another flavoprotein ; its existence was first 

 recognised by Ratner et al.^^ It occurs in liver and kidney, and 

 catalyses the oxidation of glycine to glyoxylic acid and ammonia, and 

 of sarcosine to glyoxylic acid and methylamine. As isolated from 

 lamb, cat and human kidneys, glycine oxidase showed no tendency to 

 dissociate except in acid solution, but the enzyme from pig kidney 

 was very unstable, and this was shown to be due to a factor in pig 

 kidney, possibly enzymic in nature. Exactly the same behaviour was 

 observed with D-amino acid oxidase from pig kidney and kidneys 

 from other species. Unfortimately the early work on amino acid 

 oxidase was done with preparations from pig kidney and the report 

 that it was completely dissociated at neutral pYi values must, there- 

 fore, be accepted with reserve. 



Diamino Oxidase 



Di- and poly-amines, such as histamine, cadaverine and spermine, 

 are converted into amino aldehydes by an enzyme similar to, but 

 apparently not identical with, amino acid oxidase. ^^ The enzyme was 

 purified by M. Laskowski.^^ Histaminase contains flaviiie adenine 

 dinucleotide.^^" 



Quinine Oxidase 



Ribofiavine was also present in an enzyme from rabbit liver that 

 oxidised quinine and other quinoline derivatives to their carbo- 

 styrils. Isoquinolines, some pyridine derivatives and N^-methyl- 

 nicotinamide were also oxidised. ^^ 



196 



