The Species and Heme Pocket Properties of Sturgeon Hemoglobins Upon Interaction with N-dodecyl Trimethylammonium Bromide

Abstract

The variations in fish hemoglobin (Hb) structures play a vital role in their respiratory performance under various environmental conditions and are impacted by their physiological properties. The major hemoglobins from two species of sturgeon were studied upon interaction with n-dodecyl trimethyl ammonium bromide (DTAB) using the UV-vis absorption, circular dichroism (CD), fluorescence spectroscopy, and oxygen affinity measurement methods as well as chemometric analysis. The UV-Vis absorption spectra between 500 and 650 nm was used to identify each species of hemoglobin, and to show that the concentration of oxyHb and metHb decreases, while that of deoxyHb increases upon interaction with DTAB. Both reduced oxyHb and oxidized hemichrome of the two Hbs were studied to obtain information about the DTAB efects on their structural features. The circular dichroism (CD) was utilized to obtain secondary structure and compactness for Hb upon interaction with DTAB. Binding of DTAB molecules induced the unfolding of Hb, and was accompanied with exposure of the heme pocket facilitating its oxidation. The differences between unfolding processes for the two Acipenser species were indicated by fluorescence spectroscopy. The chemometric analysis of Hbs was investigated upon interaction with DTAB under titration, using fluorescence spectra allowing determination of the number of components and mole fractions of the oxidized Hb. Our data showed that Acipenser persicus Hb had a more hyperchromic character, more surface area, more loosely folded structure, and therefore, exposed region of heme group compared with Acipenser stellatus oxyHb. In addition, with increasing DTAB the transition of Acipenser stellatus oxyHb to the state of hemichrome occurred at a slower speed than Acipenser persicus oxyHb, and finally more oxygen affinity and compactness. Our results suggest that these differences aroused from the inherent differences between the heme groups which fulfil a potentially important physiological role in these fish.