Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nitrate reductase (NR) (EC 1.6.6.1) activity and NR activation state, i.e. activity in the presence of Mg(2+) relative to activity in the absence of Mg(2+), in cucumber (Cucumis sativus) leaves increased in the light and decreased in the dark. In contrast to leaves, NR activation state in the roots did not show light/dark-dependent changes. Root NR was activated by anoxia or by addition of uncoupler (CCCP) or mannose. These treatments decreased ATP levels in root tissue. On the contrary, high oxygen supply promoted some NR inactivation. When an extract from anoxic roots was preincubated with ATP, NR was gradually inactivated. Subsequent addition of 5'-AMP resulted in a remarkable reactivation of the enzyme. NR extracted from hyperoxygenated roots was activated by preincubation with 5'-AMP, and the process was reversed by ATP. These results suggest the participation of adenine nucleotides on the in vivo modulation of NR activity in cucumber roots. NR was activated in vivo by cellular acidification and inactivated by alkalinisation. The acid-induced activation of NR was greatly prevented by okadaic acid, a protein phosphatase inhibitor. Our data indicate that, as in barley roots, anoxia, uncouplers, and mannose feeding activate cucumber root NR, at least partly, by enhancing NR dephosphorylation via a decrease in the internal level of ATP and a concomitant cellular acidification.
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PMID:Modulation of nitrate reductase activity in cucumber (Cucumis sativus) roots. 1144 53

Previously, it has been shown that treatment of Paracoccus denitrificans cells with phenylglyoxal inhibits the methyl-viologen-linked nitrate reductase activity by blocking the nitrate transporter. This inhibition disappears if tetraphenylphosphonium cation (TPP(+)) is added to the assay medium. In the present paper, the following evidence suggests that the effect of TPP(+) results from an increased transmembrane anion permeability and not from transporter reactivation or cell lysis. (1) Beside nitrate, TPP(+) also mediated the utilisation of chlorate, which normally lacks access to the cytoplasm. (2) The TPP(+) pathway had about hundred-times higher K(m) values for nitrate and chlorate than nitrate reductase in Triton X-100 permeabilised cells. (3) Although the uncoupler CCCP alone failed to overcome the PG block, it stimulated the operation of the TPP(+) pathway. (4) The method of continuous variations allowed the transport stoichiometry TPP(+)/NO(3)(-) to be determined as 3, indicating charge compensation for nitrate movement and the subsequent transmembrane two-electron redox reaction. Anion uptake was also measured independently from passive swelling of uncoupled spheroplasts in iso-osmotic solutions of ammonium salts. The permeability to nitrate lay in the permeability sequence Cl(-)<NO(3)(-)<ClO(4)(-)<SCN(-) and was further enhanced by TPP(+).
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PMID:Passive penetration of nitrate through the plasma membrane of Paracoccus denitrificans and its potentiation by the lipophilic tetraphenylphosphonium cation. 1261 55