Spectrosopic studies of an insect hemoglobin from the backswimmer Buenoa margaritacea (hemiptera:notonectidae)

Hemoglobin (Hb) isolated from the backswimmer Buenoa margaritacea has been analyzed spectroscopically. The met form at pH < 6 shows a 30nm red shift in the Q_v and Q_o bands and a 5nm red shift in the Soret band compared to mammalian Hb, while only minor differences are seen in the spectra of the CO and O₂ adducts of Hb from Buenoa and mammals. EPR spectra of the metHb show a superposition of signals; at low pH they are mainly of axial high-spin character, while at high pH a low-spin signal predominates with an O-type g-tensor (2.54, 2.61, 1.85) comparable to that of hydroxy myoglobin. Infrared spectra of Hb¹²C-¹⁶O at pH 8.2 reveal two major absorption bands at 1934 cm^-1 and 1967 cm^-1, which shift to 1892 cm^-1 and 1923 cm^-1, respectively, for Hb¹²C-¹⁸O. As isolated the Buenoa Hb consists of several isozymes, all of which have a histidine as the proximal ligand of the heme iron.