The reaction of nitrite with the haemocyanin of the Roman snail (Helix pomatia)

Abstract

The reaction of nitrite at pH 5.0-7.0 with the deoxyhaemocyanin of a mollusc, the Roman snail (Helix pomatia), yielded nitrosylhaemocyanin (CuIA.NO+ CuIIB), in contrast with the formation of methaemocyanin with the deoxyhaemocyanin of the crustacean Astacus leptodactylus (mud crayfish). With Helix haemocyanin 1 NO was thereby liberated per active site, as shown by m.s., as against 2 NO with Astacus haemocyanin. Helix nitrosylhaemocyanin was characterized in c.d. by the negative extremum at 336 nm (CuIA.NO+) and by the mononuclear e.p.r. signal at g = 2 (CuIIB). Binuclear e.p.r. signals have been observed after the addition of nitrite to methaemocyanins. With Astacus methaemocyanin, no further reaction occurred, whereas with Helix methaemocyanin the mononuclear e.p.r. signal, characteristic for nitrosylhaemocyanin gradually appeared. This formation of Helix nitrosylhaemocyanin implicates the binding, most likely on CuIIA, of a second nitrite besides a bridging nitrite, so that a dismutation into NO and NO2 can occur there. A further dismutation of NO2 yields nitrite and nitrate. The formation of the latter was demonstrated by Raman spectrometry. The reaction rate of Helix methaemocyanin with nitrite decreased with increasing pH according to the Henderson-Hasselbalch equation with a pKa value of 6.77, attributed to a mu-aquo bridging ligand, which can be exchanged for nitrite, in equilibrium with a mu-hydroxo ligand which cannot. These data also favour the formulation of the final reaction product as nitrosylhaemocyanin instead of semi-methaemocyanin, with or without bound nitrite.

Nitrite Reductase Activity of Deoxy Carcinus maenas Hemocyanin: Formation of the Half-Met Derivative

“…Thus, the reaction can be written as in Scheme 1 where nitrite is a single electron oxidant of the binuclear active site. The proposed reaction scheme is based on a material balance of reactants and products and is in accord with the observation of a pH dependence for GHM−Hc formation using excess nitrite , and with the identification of NO formed in the reaction. , …”

“…The reaction of nitrite with the binuclear copper protein hemocyanin (Hc) leads to the formation of a partially oxidized (half-met) Cu I −Cu II Hc, or fully oxidized (met) Cu II −Cu II Hc, where the oxidation state of the protein derivative depends on its animal source and the reaction conditions employed. − Nitric oxide (NO) is another product of this reaction. , In the presence of excess nitrite, a green half-met (GHM) derivative, in which nitrite is bound to Cu(II), , is produced in molluscan Hcs as well as in the arthropodan Hc from Carcinus maenas . When Astacus leptodactylus (arthropoda) Hc is reacted with excess nitrite, met-Hc is formed, together with two equivalents of NO 4 consistent with two, single-electron steps during oxidation of the protein.…”

“…When Astacus leptodactylus (arthropoda) Hc is reacted with excess nitrite, met-Hc is formed, together with two equivalents of NO 4 consistent with two, single-electron steps during oxidation of the protein. When deoxy Helix pomatia (mollusca) Hc is reacted with excess nitrite, it is suggested that the initial product is also met-Hc, which reacts again with nitrite to yield GHM-Hc. In order to initially form met-Hc through a two-electron oxidation of deoxy Hc, the chemistry requires that 2 equiv of NO are formed.…”

Saliva nitrite is higher in male children with autism spectrum disorder and positively correlated with serum nitrate

“…According to the nitrate-nitrite-NO pathway, levels of NO in saliva and serum are regulated by multiple factors, at least including production, consumption, transportation and reabsorption of different nitrogen-containing anions and gas molecules [ 68 ]. Under aerobic conditions, nitrite may be generated from NO oxidation catalyzed by copper enzyme ceruloplasmin [ 69 ], dismutation of nitrogen dioxide (NO 2 ) [ 70 ], hydration of dinitrogen trioxide (N 2 O 3 ) [ 71 ], or reduction of nitrate catalyzed by commensal bacterial nitrate reductase in oral cavity or gastrointestine [ 67 ]. Consumption of nitrite may go through reduction to NO catalyzed by multiple nitrite reductases, or oxidation to nitrate catalyzed by oxygenated heme proteins [ 72 ].…”

A comparison of survivourship and function (grazing and behaviour) of three gastropod species used as clean-up crew for the marine aquarium trade

“…These initial increases in nitrite probably resulted from the early mortality events within the tanks briefly overwhelming a biological filtration system that was not fully competent to convert nitrite to nitrate at that time. Nitrite is known to be toxic to invertebrates as it removes the ability of pigments to carry oxygen [ 27 ], as demonstrated by Cheng and Chen [ 28 ] through the inverse relationship between nitrite concentration and oxyhaemocyanin levels (oxygen carrier common to both arthropods and molluscs [ 29 ]). Increasing concentrations of nitrite have also been shown to lower the amount of food eaten in other gastropods such as the greenlip abalone Haliotis laevigata [ 30 ].…”