title: A membrane-associated protein with Cr(VI)-reducing activity from Thermus scotoductus SA-01.
abstract: A membrane-associated chromate reductase from Thermus scotoductus SA-01 has been purified to apparent homogeneity and shown to couple the reduction of Cr(VI) to NAD(P)H oxidation, with a preference towards NADH. The chromate reductase is a homodimer with a monomeric molecular weight of 48 kDa and a noncovalently bound FAD coenzyme. The enzyme is optimally active at a pH of 6.5 and 65 degrees C with a K(m) of 55.5+/-4.2 microM and a V(max) of 2.3+/-0.1 micromol Cr(VI) min(-1) mg(-1) protein. The catalytic efficiency (k(cat)/K(m)) of the enzyme was found to be comparable to that found for quinone reductases but more efficient than the nitroreductases. N-terminal sequencing and subsequent screening of a genomic library of T. scotoductus revealed an ORF of 1386 bp, homologous (84%) to the dihydrolipoamide dehydrogenase gene of Thermus thermophilus HB8. These results extend the knowledge of chromate reductases mediating Cr(VI) reduction via noncovalently bound or free redox-active flavin groups and the activity of dihydrolipoamide dehydrogenases towards physiologically unrelated substrates.
authors.affiliation: Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, Bloemfontein, South Africa.
authors.forename: Diederik Johannes
authors.initials: DJ
authors.lastname: Opperman
authors.forename: Esta
authors.initials: E
authors.lastname: van Heerden
mesh_terms: D002857:Chromium / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000378:metabolism; D009252:NADPH Dehydrogenase / Q000235:genetics*; D010088:Oxidoreductases / Q000378:metabolism*; D013824:Thermus / Q000201:enzymology* / Q000235:genetics
chemical_list: D008565:Membrane Proteins; D002857:Chromium; D010088:Oxidoreductases; D009252:NADPH Dehydrogenase; C063243:chromate reductase