Abstract
Hemin (ferric protoporphyrin IX chloride) in the presence of hydrogen peroxide or
tert-butyl hydroperoxide was found to cleave folic acid at the C
9N
10 bond. The ferrous form of hemin was not involved in hydroperoxide-dependent folic acid degradation, as indicated by the lack of inhibition by carbon monoxide. Molecular oxygen was not required for the degradation. GSHMn(II) or NAD(P)H in the presence of molecular oxygen did not support hemin-mediated folic acid degradation. The degradation increased as the temperature was elevated from 10 to 70 °C. Ascorbic acid and azide were potent inhibitors. Superoxide dismutase and hydroxyl radical quenchers, such as ethanol, mannitol, benzoate, and dimethyl sulfoxide did not inhibit the reaction. Catalase inhibited hydrogen peroxide-supported degradation but not the
tert-butyl hydroperoxide-dependent one. Thiol compounds, such as thioglycolic acid, thiourea, glutathione, cysteine, and 2-mercaptoethanol, inhibited the hydrogen peroxide-dependent degradation but supported the
tert-butyl hydroperoxide-mediated one.
N
5-formyl tetrahydrofolic acid, but not
N
10-formyl folic acid, was degraded by hemin in the presence of H
2O
2 or TBHP. The data obtained are suggestive of a mechanism similar to
N-demethylation reactions catalyzed by cytochrome
P-450 and some peroxidases.