Structural basis of the lactate-dependent allosteric regulation of oxygen binding in arthropod hemocyanin.

Hemocyanin (Hc) is an oxygen carrier protein in which oxygen binding is regulated by allosteric effectors such as H(+) and L-lactate. Isothermal titration calorimetric measurements showed that L-lactate binds to dodecameric and heterohexameric Hc and to the CaeSS3 homohexamer but not to the CaeSS2 monomer. The binding of lactate caused no change in the optical absorption and x-ray absorption spectra of either oxy- or deoxy-Hc, suggesting that no structural rearrangement of the active site occurred.

Correlation between hemichrome stability and the root effect in tetrameric hemoglobins.

Oxidation of Hbs leads to the formation of different forms of Fe(III) that are relevant to a range of biochemical and physiological functions. Here we report a combined EPR/x-ray crystallography study performed at acidic pH on six ferric tetrameric Hbs. Five of the Hbs were isolated from the high-Antarctic notothenioid fishes Trematomus bernacchii, Trematomus newnesi, and Gymnodraco acuticeps, and one was isolated from the sub-Antarctic notothenioid Cottoperca gobio.

Aspects of structure and bonding in copper-amino acid complexes revealed by single-crystal EPR/ENDOR spectroscopy and density functional calculations.

This work deduces from a series of well-defined copper-doped amino acid crystals, relationships between structural features of the copper complexes, and ligand-bound proton hyperfine parameters. These were established by combining results from electron paramagnetic resonance (EPR)/electron-nuclear double resonance (ENDOR) studies, crystallography, and were further assessed by quantum mechanical (QM) calculations. A detailed evaluation of previous studies on Cu(2+) doped into alpha-glycine, triglycine sulfate, alpha-glycylglycine, and L-alanine crystals reveal correlations between geometric features of the copper sites and proton hyperfine couplings from amino-bound and carbon-bound hydrogens.

Molecular basis of the Bohr effect in arthropod hemocyanin.

Flash photolysis and K-edge x-ray absorption spectroscopy (XAS) were used to investigate the functional and structural effects of pH on the oxygen affinity of three homologous arthropod hemocyanins (Hcs). Flash photolysis measurements showed that the well-characterized pH dependence of oxygen affinity (Bohr effect) is attributable to changes in the oxygen binding rate constant, k(on), rather than changes in k(off). In parallel, coordination geometry of copper in Hc was evaluated as a function of pH by XAS.