CATABOLISM OF PTERIDINE COFACTORS .2. A SPECIFIC PTERIN DEAMINASE IN RAT LIVER

A specific pterin deaminase has been detected in rat liver. The enzyme was purified 23-fold. During its purification, guanine deaminase (EC 3.5.4.3) activity of the protein was increased 39-fold. Evidence is given which establishes the nonidentity of pterin deaminase and guanine deaminase: changes in the ratio of their activities during preparation; differences in stability during storage and inhibition by CN- and by azaguanine and guanine; differences in the pH maxima and in the distribution of enzyme activities in various organisms. The reaction maximum is at pH 6.5 and Km is 30 μM. The enzyme specifically deaminates pterin, isoxanthopterin and tetrahydropterin. Xanthopterin, biopterin, neopterin, pterin-6-carboxylic acid, and 6-hydroxymethylpterin are not deaminated. In the honeybee (Apis mellifica), pterin deaminase activity has also been detected. The highest activity has been found in 4-day-old larvae. © 1969.