Inactivation by acetylene of spinach nitrate reductase

Characterization of the Reversible Inactivation of Ankistrodesmus braunii Nitrate Reductase by Hydroxylamine

“…The fact that NH20H inactivation depends on initial concentrations of NO3 and progresses during the enzymic assays (Fig. 2) (20,28). The most plausible interpretation is that the inactivating agents, NH20H, Plant Physiol.…”

“…To reversibly inactivate NR in vitro, both the absence of N03 and reducing conditions were absolutely required. In addition, it was also proved that the presence of chemicals like 02 and acetylene accelerated the inactivation process (2,3,7,20). The reactivation was readily achieved by ferricyanide, presumably as a consequence of the oxidation of some overreduced state of the molybdenum domain of the enzyme (7,23,28).…”

“…NR was purified essentially according to the procedure described by De la Rosa et al (8) (20). NADH-dehydrogenase activity was assayed by measuring the reduction of DCIP at 600 nm (26).…”

“…MV*-NR was estimated by two methods. When MV was reduced by Na2S204, NR was monitored by colorimetrically measuring NO2- (20). In the experiments in which NR was incubated in the presence of Na2S204 and NH20H, these NO2-measurements were corrected for the NO2-formed by the chemical reaction between those two compounds.…”

“…To reduce MV electrochemically, 0.14 mM MV in 50 mm K-phosphate, pH 7.5, was stirred over a cathode of Hg at a redox potential of -0.5 V according to Thorneley (27) (6), using BSA as a standard. NO2-was measured by the diazo-coupling colorimetric assay (20). Spectrophotometric measurements were carried out in a Bausch and Lomb Spectronic 2000 spectrophotometer.…”