A purine N1-C6 hydrolase activity in the chicken egg yolk: a vestigial enzyme?

All attempts to prove the presence of xanthine oxidase and uricase in yolk preparations failed. We were able instead to show that yolk preparations could hydrolyze the N1-C6 bond of certain purine bases. In the case of xanthine, 4-ureido-imidazole-5-carboxylic acid and 4-ureido-imidazole are formed. Activity only becomes apparent during purification. An analogous enzyme was described earlier in Clostridium cyclindrosporum. The liver and the blood plasma of actively laying hens do not contain the enzyme. A scheme for the degradation of egg ribonucleic acids is presented.