Characterization of crystalline formate dehydrogenase from Candida methanolica

The crystalline formate dehydrogenase from Candida methanolica, which showed the highest specific activity (7.52 U/mg) so far reported, was characterized in detail. The enzyme is a dimer composed of identifical subunits, each containing one SH group related to the catalytic activity. The molecular mass of the enzyme is about 82–86 kDa. The K_m values were found to be 3.0 mM for formate and 0.11 mM for NAD⁺. Even if the enzyme was incubated at pH 6.5–9.5 or at 55°C, the activity remained at 100%. Hg²⁺, Ni²⁺, NaCN, NaN₃ and p‐chloromercuribenzoate strongly inhibited the enzyme activity, while the enzyme showed relatively high resistance to various chelating agents. The amino acid composition and some other physicochemical properties of the enzyme were studied. Immunological studies revealed that formate dehydrogenases of methanol‐utilizing yeasts immunologically more or less resemble each other, but differ from those of methanol‐utilizing bacteria. Furthermore, yeast formate dehydrogenases can be immunologically classified into three types: (a) the Candida type, (b) the Torulopsis/Hansenula/Pichia type and (c) the formaldehyde‐resistant yeast type. For simple and large‐scale preparation of the enzyme for practical use, treatment of cells of C. methanolica with the commercial cationic detergent, ‘Benzalkonium’ cation, is useful: the total and specific activities of the enzyme are 1.17‐fold and 3.10‐fold higher than those of the crude cell‐free extract, respectively.