Oxygen transport proteins: II. Chemical and spectroscopic properties of scorpion ( Buthus sindicus) native hemocyanin and purified subunit Bsin1

Abstract

Out of eight different polypeptide chains, present in the native hemocyanin molecule of scorpion Buthus sindicus, subunit Bsin1 was preparatively purified and characterized by amino acid composition, laser desorption mass spectrometry and spectroscopic techniques. Thermal stability of the intact respiratory protein and its subunit was studied by following the change in ellipticity at 222 nm as a function of temperature. The copper-dioxygen system at the binuclear active site has a stabilizing effect and the oxy-proteins are significantly more thermostable than the apo-forms. The thermal stability of the scorpion Hc from B. sindicus is considerably smaller than that of the tarantula ( Eurypelma californicum) Hc [Sterner R et al., FEBS Lett 1995;364:9–12], although both, scorpion and spider, belong to the subphylum chelicerata. The fluorescence properties of the scorpion Hc and Bsin1 suggest that the indol groups are in rather nonpolar environment, deeply ‘buried’ in the interior of the aggregates and structural subunits. At the same time, these chromophores are located on subunit interfaces in the C. sapidus and O. vulgaris Hcs, participating in protein–protein interactions [Ricchelli F et al., Arch Biochem Biophys 1984;235:461–469; Stoeva S et al., Spectrochimica Acta A 1995;51:1965–1974].