The reaction of nitrite with the haemocyanin of Astacus leptodactylus

Abstract

The reaction of nitrite at pH 5.7 with deoxyhaemocyanin of Astacus leptodactylus yielded methaemocyanin in two one-electron steps, as nitrite was reduced to NO. This methaemocyanin could be almost fully regenerated by an anaerobic treatment with HONH2, in contrast with the methaemocyanin prepared with H2O2. A destruction of active sites on treating oxyhaemocyanin with HONH2 explains the partial regeneration of methaemocyanin under air, as traces of H2O2 are formed in the autoxidation of HONH2. The reaction rate of nitrite with deoxyhaemocyanin is almost 15 times that with oxyhaemocyanin. The slope of -1.0 for the logarithm of the pseudo-first-order rate constants plotted against pH indicates that HNO2 is the reacting species. Methaemocyanin was e.p.r.-undetectable, but a binuclear signal was observed at g = 2 on binding nitrite to methaemocyanin. This signal disappeared with a pKa of 6.50, suggesting that a mu-aquo bridging ligand, which can be replaced by nitrite, is deprotonated to a mu-hydroxo bridging ligand, which resists substitution by nitrite. The intensity of this triplet e.p.r. signal allowed the determination of the association constant of nitrite to the active site of Astacus methaemocyanin and yielded a value of 237 M-1 at pH 5.7. The interpretation by some authors of nitrosylhaemocyanin as a nitrite derivative of semimethaemocyanin is contradicted by this rapid reaction of nitrite with copper(I) in deoxyhaemocyanin and in semi-methaemocyanin and by the low binding constant of nitrite to the active site of methaemocyanin.

Total metal levels in crayfish Astacus leptodactylus (Eschscholtz, 1823), and surface sediments in Lake Terkos, Turkey

“…As a regulating metal for freshwater decapods, copper has a significant biochemical role since it constitutes a part of hemocyanin that is a respiratory protein and binds oxygen in arthropods and mollusks (Tahon et al 1988;Mackevičienė 2002). According to the Cu values determined in this study, the highest values were seen in hepatopancreas followed by gills.…”

Effect of nitrite on immunity of the white shrimp Litopenaeus vannamei at low temperture and low salinity

“…(Yavuzcan Yildiz and Benli 2004). In an in vitro study using A. leptodactylus, Tahon et al (1988) found that the reaction of nitrite with deoxyhemocyanin was 5 times more than with oxyhemocyanin, and finally formed methemocyanin. Oxyhemocyanin of P. monodon exposed to nitrite at 0.36 mmol/l was significantly decreased (Cheng and Chen 1999), and Li et al (2007) reported haemolymph oxyhemocyanin content was higher at 3.0 % than that at 17 and 32 %.…”

The effects of nitrite on the excitability of brain neurons in the common snail

“…The common snail has no hemoglobin, though the hemolymph contains hemocyanin, which, like hemoglobin, can be in the reduced or the oxidized form [4]. The oxidized forms of hemocyanin and other invertebrate respiratory proteins, like deoxyhemoglobin, have nitrite reductase activity [17,19], i.e., they can interact with nitrite ions, leading to the development of hypoxia on the one hand and to increases in NO contents on the other. In mollusks, like higher animals, hypoxia induces depolarization and increases neuron activity [ii1.…”