| Abstrakt: |
Highly purified preparations of thymine 7-hydroxylase from Neurospora crassa catalyzed the decarboxylation of alpha-ketoglutarate but yielded no hydroxylated product when uracil was substituted for thymine in the standard incubation mixture. Although the uracil-dependent decarboxylation was much slower than the coupled reaction, both reactions were similar with respect to the requirement for molecular oxygen, the stoichiometric formation of succinate, and the stimulations effected by Fe2+, ascorbate, and catalase. That the same enzyme catalyzed both reactions was indicated by the parallel loss of the uracil- and thymine-dependent activities upon heat denaturation, their copurification, and the lower level of both activities in a mutant strain deficient in the 7-hydroxylase. These data are consonant with molecular oxygen initially attacking alpha-ketoglutarate in the thymine 7-hydroxylase reaction. |
