Maize glutathione-dependent formaldehyde dehydrogenase: protein sequence and catalytic properties

Glutathione-dependent formaldehyde dehydrogenase (FDH; EC 1.2.1.1) has been purified 3900-fold from maize cell-suspension cultures to a specific activ ity of 4.68 mu mol (mg protein)(-1) min(-1). The homogeneous enzyme consist ed of two identical subunits with a molecular mass of 42 kDa, and an isoele ctric point of 5.8. Eight tryptic peptides were sequenced and gave a perfec t fit to the protein sequence derived from maize Fdh cDNA (J. Fliegmann and H. Sandermann, 1997, Slant Mol Biol 34: 843-854). There was 62% identity w ith the eucaryotic FDH consensus sequence. Michaelis constants of approx. 2 0 mu m (formaldehyde), approx; 50 mu m (glutathione) and approx. 31 mu m (N AD(+)) were determined for the maize enzyme as well as for FDH partially pu rified from dog lung. Besides S-hydroxymethylglutathione, pentanol-1, octan ol-1, and omega-hydroxy-fatty acids served as substrates for both FDH prepa rations. The unusual substrate specificity indicates that FDH may be involv ed in the detoxification of long-chain lipid peroxidation products.