期刊
FEMS MICROBIOLOGY LETTERS
卷 280, 期 2, 页码 210-218出版社
OXFORD UNIV PRESS
DOI: 10.1111/j.1574-6968.2007.01063.x
关键词
Cr(VI); chromate reductase; dihydrolipoamide dehydrogenase; Thermus scotoductus; metal reduction; flavoprotein
类别
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 mu M and a V-max of 2.3 +/- 0.1 mu mol 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.
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