Purification and Characterization of S-Formylglutathione Hydrolase from Human, Rat and Fish Tissues

Formaldehyde is oxidized in mammalian tissues and in several other sources to formate in two consecutive reactions catalyzed by separate enzymes (Uotila and Koivusalo, 1974a; 1974b) (Scheme 1). Formaldehyde and glutathione react first non-enzymically to form a hemithioacetal adduct (S-hydroxymethylglutathione) (Reaction 1). The adduct is the substrate of formaldehyde dehydrogenase (EC 1.2.1.1) and is oxidized in the NAD-depend-ent reaction to S-formylglutathione (Reaction 2). Formaldehyde dehydrogenase has been shown to be identical with the class III alcohol dehydrogenase (Koivusalo et al., 1989). For a comprehensive review on formaldehyde dehydrogenase, see Uotila and Koivusalo (1989). The hydrolysis of S-formylglutathione to reduced glutathione and formate (Reaction 3) is catalyzed by a specific enzyme, S-formylglutathione hydrolase (EC 3.1.2.12). Formate can be oxidized by the catalase reaction or is transferred to tetrahydrofolate to form 10-formyl-tetrahydrofolate. Formate is thus incorporated into the reactions of the C-1 metabolism by which it can be oxidized to carbon dioxide in the 10-tetrahydrofolate dehydrogenase reaction (Kutzbach and Stokstad, 1968).