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

Abstract

The

HYDROXYLAMINE METABOLISM IN MONORAPHIDIUM BRAUNII

“…In cells that were darkened after the addition of NH2OH, the levels of NADH-nitrate reductase remained low. As when tested in vitro with purified nitrate reductase (Balandin et al, 1986), in vivo, NH2OH did not inhibit the diaphorase activity. The in situ inactivation of nitrate reductase by NH2OH was extremely rapid.…”

“…braunii nitrate reductase caused by NHgOH. Our results indicate that nitrate reductase in ;ts reduced form has a high affinity for NH2OH which becomes bound to the active site for nitrate thus impairing both the overall and the terminal activities without affecting the dehydrogenase activity Balandin, Fernandez & Aparicio, 1986).…”

“…Although the in vitro inactivation of nitrate reductase has been characterized using chemicals like cyanide (Vennesland, 1981) and NHgOH (Balandin et al, 1986), the mechanism of inactivation that operates in vivo is still unknown (Larsson, Larsson & Guerrero, 1985). However, the activation of nitrate reductase by blue light both in vitro and in vivo has been clearly established in C. reinhardii (Azuara & Aparicio, 1985).…”

“…To stop the reaction and to remove NADH and other factors that interfere with the diazotization reaction, zinc acetate and phenazine methosulphate were added to the reaction mixture (Scholl, Harper & Hageman, 1974). Methyl viologen (MV*)-nitrate reductase activity was estimated by nitrite formation, and NADH-diaphorase using DCPIP as previously described (Balandin et al, 1986). Nitrite reductase was determined according to Losada & Paneque (1971).…”

HYDROXYLAMINE METABOLISM IN MONORAPHIDIUM BRAUNII

“…Recently, we have shown that NHgOH reversibly inactivates nitrate reductase from Monoraphidium hraunii. The NHgOHinactivated enzyme readily reactivated upon irradiation with blue light in the presence of flavins (Aparicio et al, 1985;Balandin, Fernandez & Aparicio, 1986). Although NH2OH might not be the physiological putative compound that inactivates in situ nitrate reductase, the results presented in this paper and the following one may contribute to a better understanding of the regulation of inorganic nitrogen metabolism in green algae.…”