Purification and characterization of the periplasmic nitrate reductase from Thiosphaera pantotropha
Open Access
- 1 February 1994
- journal article
- Published by Wiley in JBIC Journal of Biological Inorganic Chemistry
- Vol. 220 (1), 117-124
- https://doi.org/10.1111/j.1432-1033.1994.tb18605.x
Abstract
The periplasmic nitrate reductase of Thiosphaera pantotropha has been purified from a mutant strain (M-6) that overproduces the enzyme activity under anaerobic growth conditions. The enzyme is a complex of a 93-kDa polypeptide and a 16-kDa nitrate-oxidizable cytochrome c552. The complex contains molybdenum; a fluorescent compound with spectral features of a pterin derivative can be extracted. In contrast to the dissimilatory membrane-bound nitrate reductases, the periplasmic nitrate reductase shows high specificity for nitrate as a substrate and is insensitive to inhibition by azide. The 93-kDa subunit exhibits immunological cross-reactivity with the catalytic subunit of Rhodobacter capsulatus N22DNAR+ periplasmic nitrate reductase. Mass spectrometric comparisons of holo-cytochrome c552 and apo-cytochrome c552 demonstrated that the polypeptide bound two haem groups. Mediated redox potentiometry of the cytochrome indicated that the haem groups have reduction potentials (pH = 7.0) of approximately −15 mV and +80 mV. The functional significance of these potentials is discussed in relation to the proposed physiological role of the enzyme as a redox valve.Keywords
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