The effect of low oxygen tension on the activity of aerobic dehydrogenases

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Abstract
The oxidation of D-alanine, hypoxanthine and glucose by D-amino-acid oxidase, xanthine oxidase and glucose oxidase (notatin) respectively has been studied at O 2 tensions varying from 1 to 100 %, mainly with a view to examining enzyme activity at an O 2 tension comparable to that obtaining in the animal body, i.e. < 10 % O 2 . It was found that ( a ) the rate of substrate oxidation decreases markedly at O 2 tensions < 20 % , i.e. the enzymes examined have a low O 2 affinity; ( b ) the substrate concentration giving half-maximal oxidation rate (= Michaelis constant, K m ) decreases with a lowering of the O 2 tension; ( c ) the rate of primary substrate oxidation at low O 2 tension in presence of catalase is higher than in presence of catalase and a secondary substrate which undergoes peroxidatic oxidation by catalase and H 2 O 2 . A possible mechanism underlying this effect, which involves the participation of catalase and H 2 O 2 in primary substrate oxidation at low O 2 tension, is suggested.