{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,26]],"date-time":"2026-08-26T17:52:13Z","timestamp":1787766733455,"version":"build-2784847793"},"reference-count":0,"publisher":"Portland Press Ltd.","issue":"3","content-domain":{"domain":["portlandpress.com"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[1978,6,1]]},"abstract":"<jats:p>Low-temperature e.p.r. spectra are presented of nitrite reductase purified from leaves of vegetable marrow (Cucurbita pepo). The oxidized enzyme showed a spectrum at g=6.86, 4.98 and 1.95 corresponding to high-spin Fe3+ in sirohaem, which disappeared slowly on treatment with nitrite. The midpoint potential of the sirohaem was estimated to be \u2212120mV. On reduction with Na2S2O4 or Na2S2O4+Methyl Viologen a spectrum at g=2.038, 1.944 and 1.922 was observed, due to a reduced iron\u2013sulphur centre. The midpoint potential of this centre was very low, about \u2212570mV at pH8.1, decreasing with increasing pH. On addition of cyanide, which binds to haem, and Na2S2O4, the iron\u2013sulphur centre became further reduced. We think that this is due to an increased midpoint potential of the iron\u2013sulphur centre. Other ligands to haem, such as CO and the reaction product NH3, had similar but less pronounced effects, and also changed the lineshape of the iron\u2013sulphur signal. Samples were prepared of the enzyme frozen during the reaction with nitrite, Methyl Viologen and Na2S2O4 in various proportions. Signals were interpreted as due to the reduced iron\u2013sulphur centre (with slightly different g values), a haem\u2013NO complex and reduced Methyl Viologen. In the presence of an excess of nitrite, the haem\u2013NO spectrum was more intense, whereas in the presence of an excess of Na2S2O4 it was weaker, and disappeared at the end of the reaction. A reaction sequence is proposed for the enzyme, in which the haem\u2013NO complex is an intermediate, followed by other e.p.r.-silent states, leading to the production of NH4+.<\/jats:p>","DOI":"10.1042\/bj1710519","type":"journal-article","created":{"date-parts":[[2015,8,10]],"date-time":"2015-08-10T20:10:52Z","timestamp":1439237452000},"page":"519-526","update-policy":"https:\/\/doi.org\/10.1042\/crossmark_policy","source":"Crossref","is-referenced-by-count":41,"title":["Electron-paramagnetic-resonance studies of the mechanism of leaf nitrite reductase. Signals from the iron\u2013sulphur centre and haem under turnover conditions"],"prefix":"10.1042","volume":"171","author":[{"given":"Richard","family":"Cammack","sequence":"first","affiliation":[{"name":"1Department of Plant Sciences, University of London King's College, 68 Half Moon Lane, London SE24 9JF, U.K."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dereck P.","family":"Hucklesby","sequence":"additional","affiliation":[{"name":"2Department of Plant Sciences, University of London King's College, 68 Half Moon Lane, London SE24 9JF, U.K."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eric J.","family":"Hewitt","sequence":"additional","affiliation":[{"name":"3University of Bristol, Long Ashton Research Station, Bristol BS18 9AF, U.K."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"288","container-title":["Biochemical Journal"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/portlandpress.com\/biochemj\/article-pdf\/171\/3\/519\/625739\/bj1710519.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/portlandpress.com\/biochemj\/article-pdf\/171\/3\/519\/625739\/bj1710519.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2021,11,26]],"date-time":"2021-11-26T17:49:03Z","timestamp":1637948943000},"score":1,"resource":{"primary":{"URL":"https:\/\/portlandpress.com\/biochemj\/article\/171\/3\/519\/11612\/Electron-paramagnetic-resonance-studies-of-the"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1978,6,1]]},"references-count":0,"journal-issue":{"issue":"3","published-print":{"date-parts":[[1978,6,1]]}},"URL":"https:\/\/doi.org\/10.1042\/bj1710519","relation":{},"ISSN":["0264-6021"],"issn-type":[{"value":"0264-6021","type":"print"}],"subject":[],"published":{"date-parts":[[1978,6,1]]}}}