Dihydropyrimidinase from Pseudomonas stutzeri ATCC 17588 was purified
100-fold and characterized. It was found that dihydrouracil, dihydroth
ymine and hydantoin could serve as substrates for the partially. purif
ied enzyme. The K-m values for dihydrouracil, dihydrothymine and hydan
toin were determined to be 19.6 mu M, 21.3 mu M and 36.4 mu M, respect
ively, while their respective V-max values were 0.836 mu mol/min, 0.66
6 mu mol/min and 2.21 mu mol/min. Between pH 7.5 and 9.0, enzyme activ
ity was shown to be maximal. The optimum temperature for enzyme activi
ty was 45 degrees C. Using gel filtration, the molecular weight of the
enzyme was calculated to be approximately 115000 Da. Metal ions were
found to influence the level of enzyme activity. Dihydropyrimidinase a
ctivity was stimulated by magnesium ions and inhibited by either zinc
or copper ions.