A membrane-associated protein with Cr(VI)-reducing activity from Thermus scotoductus SA-01.
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.
Opperman
Diederik Johannes
DJ
Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, Bloemfontein, South Africa.
van Heerden
Esta
E
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
D008565:Membrane Proteins; D002857:Chromium; D010088:Oxidoreductases; D009252:NADPH Dehydrogenase; C063243:chromate reductase