Electron paramagnetic resonance studies of spin-labeled hemoglobins. II. Roles of subunit interactions and of intermediate structures in the cooperative oxygenation of hemoglobin and the results of hemoglobin Yakima, hemoglobin J capetown, and carboxypeptidases A and B treated hemoglobin A

Utilizing NMR and EPR spectroscopy to probe the role of copper in prion diseases

Copper is an essential nutrient for the normal development of the brain and nervous system, although the hallmark of several neurological diseases is a change in copper concentrations in the brain and central nervous system. Prion protein (PrP) is a copper-binding, cell-surface glycoprotein that exists in two alternatively folded conformations: a normal isoform (PrP(C)) and a disease-associated isoform (PrP(Sc)). Prion diseases are a group of lethal neurodegenerative disorders that develop as a result of conformational conversion of PrP(C) into PrP(Sc). The pathogenic mechanism that triggers this conformational transformation with the subsequent development of prion diseases remains unclear. It has, however, been shown repeatedly that copper plays a significant functional role in the conformational conversion of prion proteins. In this review, we focus on current research that seeks to clarify the conformational changes associated with prion diseases and the role of copper in this mechanism, with emphasis on the latest applications of NMR and EPR spectroscopy to probe the interactions of copper with prion proteins.

Spin label probes of the environment of cysteine beta-93 in hemoglobin

The environment of cysteine beta-93 is altered during the oxygenation of hemoglobin. Electron spin resonance was used to probe the hemoglobin conformation in this crucial region on the proximal side of the heme. Spin-labeled hemoglobins in both the R-liganded state [methemoglobin and oxyhemoglobin] and the T-unliganded state [deoxyhemoglobin as well as Ni(II) and Cu(II) substituted hemoglobins] were investigated. Included in this study are iodoacetamide and maleimide labels with different constraints at the point of reaction with the SH-group, as well as a series of pyrrolidinyloxyl maleimide labels of different chain length. From differences in the correlation time of the spin labels it was possible to identify two distinct strongly immobilized configurations in addition to the relatively mobile configuration with the label on the surface of the protein. By dipolar interactions between the spin labels and paramagnetic Cu(II) at the heme center, the relative position of the three orientations for the spin label are defined. Differences are observed between the two hemoglobin conformations with respect to the relative population of the various orientations and with respect to the potential barrier associated with the reorientation of the spin labels.

Tertiary structure variability within the quaternary states of hemoglobin: a spin label study

Using variable temperature techniques, the spin label spectral resolution of hemoglobin labeled at the beta93 cysteines with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)iodonacetamide has been greatly enhanced. The effects of different ligands, inositol hexaphosphate, pH and salt concentration upon spin labeled ferrous and ferric hemoglobin indicate that the beta chain tertiary structure exhibits considerable variability within the oxy and deoxy quaternary structures. From these studies ligand and spin state changes both appear to be of significance in producing structural changes; binding of inositol hexaphosphate then produces further structural changes secondary in amplitude.

Ligand-induced conformational changes in spin label-modified human hemoglobins and chains and their carboxypeptidase A-digested derivatives

The reactive sulfhydryls of human adult and fetal hemoglobin and the single sulfhydryl of isolated gamma chains have been spin labeled with N-(1-oxyl-2,2,5,5-tetramethyl-3-pyrrolidinyl) iodoacetamide. Similar electron paramagnetic spectral differences between oxy- and deoxy-modified hemoglobins were observed for both these hemoglobins and for the isolated chains, indicating that ligand-induced conformational changes occur in isolated hemoglobin subunits as well as intact hemoglobin tetramers. Ligand induced changes in the reactivity of p-hydroxymercuribenzoate with the sulfhydryl groups of both intact hemoglobins and isolated subunits, observed by McDonald and Noble (1974) J. Biol. Chem. 249, 3161-3165), led them to draw a similar conclusion. Following carboxypeptidase A digestion of these modified hemoglobins and gamma chains, a procedure which specifically removes the two C-terminal residues of the beta or gamma chains, spectral differences between the liganded and unliganded spin-labeled derivatives still persisted. However, the magnitude of this difference was not only more reduced in the case of the hemoglobins than in that of the subunits but the spectra of both the oxy and deoxy derivatives of the hemoglobins were characteristic of the oxy derivative of a cooperative tetrameric hemoglobin. These findings support the premise that the COOH-terminal end of the beta or gamma chain contributes, although possibly to different extents, to the spectral differences exhibited by both the spin-labeled hemoglobins and chains.

Oxygen equilibrium of hemoglobin J Cape Town

Polycythemia in carriers of hemoglobin J Cape Town or hemoglobin Chesapeake is thought to be produced by increased oxygen affinity of their blood. Both hemoglobins involve substitution of amino acid residue alpha FG-4. Measurements reported here, of the oxygen equilibrium of purified hemoglobin J Cape Town, permit direct comparison of the two hemoglobins. J Cape Town exhibits lower oxygen affinity, and greater heme-heme interaction, than Chesapeake; both exhibit normal Bohr effects. Substitution of one polar amino acid residue for another of opposite charge (arginine --> glutamic acid) thus appears to create less disruption of the interface between alpha- and beta-chains than substitution of a nonpolar residue (arginine --> leucine).