Electron paramagnetic resonance studies on the molybdenum center of assimilatory NADH:nitrate reductase from Chlorella vulgaris.

Published

Journal Article

The assimilatory nitrate reductase from Chlorella contains flavin, heme, and molybdenum as prosthetic groups. The molybdenum in assimilatory nitrate reductase is associated with a pterin moiety (molybdopterin) as evidenced by the ability of the enzyme to donate active molybdenum cofactor to the Neurospora nitrate reductase mutant nit-1 and by the oxidative conversion of the pterin to two well characterized fluorescent derivatives. The properties of the molybdenum center have been examined by EPR spectroscopy. A molybdenum V signal, absent in the resting enzyme, is elicited upon reduction with NADH and abolished upon reoxidation with nitrate. Reaction of the reduced enzyme with cyanide also abolishes the molybdenum V signal. The line shape and g values of the signal show pH dependence analogous to those observed previously with hepatic sulfite oxidase. The gav for molybdenum V at pH 7.0 was 1.977 and at pH 9.0, 1.961. The signal observed at pH 7.0 exhibits interaction with a single exchangeable proton. Potentiometric titration of the molybdenum center at pH 7.0 indicates that the oxidation-reduction potentials of the molybdenum VI/V and molybdenum V/IV couples are -34 and -54 mV, respectively. These potentials are significantly different from the potentials of the molybdenum center of respiratory-type nitrate reductase and in fact quite closely resemble those of hepatic sulfite oxidase. The oxidized enzyme exhibits the EPR signal of a low spin ferric heme which is abolished upon reduction with NADH.

Full Text

Duke Authors

Cited Authors

  • Solomonson, LP; Barber, MJ; Howard, WD; Johnson, JL; Rajagopalan, KV

Published Date

  • January 25, 1984

Published In

Volume / Issue

  • 259 / 2

Start / End Page

  • 849 - 853

PubMed ID

  • 6319388

Pubmed Central ID

  • 6319388

International Standard Serial Number (ISSN)

  • 0021-9258

Language

  • eng

Conference Location

  • United States