Xanthine Oxidases in Different Species.

Abstract

The enzyme present in bird tissues was a dehydrogenase rather than an oxidase, since the aerobic activity of the enzyme was negligible in comparison with its activity in the presence of methylene blue. The enzyme present in mammalian tissues was an oxidase the aerobic activity of which could generally be increased from 1.5 to 2.5 times by the addition of methylene blue to the aerobic test system. In all cases the aerobic activity of the xanthine oxidase was inhibited 40-100% by antabuse, and this inhibition was completely overcome by the addition of methylene blue. Heating the tissue homogenate at 56[degree] for 30 min. gave decreased aerobic xanthine oxidase activities with rat and mouse liver but no change with most mammalian tissues; the antabuse inhibition was eliminated to varying degrees with different tissues. The dehydrogenase enzyme or the dehydrogenase portion of the mammalian xanthine oxidase complex was unaffected by antabuse or by the heating procedure, since the activity in the presence of methylene blue remained constant irrespective of what happened to the aerobic activity.