A characterization of ferric sulphaemoglobin

Sulphaemoglobin formation in fish: a comparison between the haemoglobin of the sulphide-sensitive rainbow trout (Oncorhynchus Mykiss) and of the sulphide-tolerant common carp (Cyprinus Carpio)

A method for the quantitative determination of sulphaemoglobin (SHb) in a mixture of haemoglobin derivatives by spectral deconvolution is described. SHb formation was studied in haemolysates and in red blood cells of the sulphide-sensitive rainbow trout (Oncorhynchus mykiss) and of the sulphide-tolerant common carp (Cyprinus carpio). Addition of sulphide caused the formation of SHb in haemolysates of both animals. However, haemoglobin from common carp was much less sensitive to sulphide than was trout haemoglobin. The maximal obtainable SHb fraction was approximately 30 % in trout and 10 % in carp haemolysates. In both animals, the SHb fraction increased with increasing Hb and sulphide concentrations up to 100 micromol l(−)(1) and 1 mmol l(−)(1), respectively, and was favoured by a low pH. An increase of temperature between 5 and 25 degrees C strongly increased SHb formation in trout haemolysate. In contrast, temperature changes had almost no effect on SHb production in carp. Within trout red blood cells, approximately 7 % of total haemoglobin was converted to SHb during 60 min of incubation (with 2.5 mmol l(−)(1) sulphide), inducing a 20 % loss of haemoglobin oxygen-saturation. In carp red blood cells incubated under identical conditions, SHb formation was minimal and haemoglobin oxygen-saturation was not affected.

A proton nuclear magnetic resonance study of sulfmyoglobin cyanide

The proton nuclear magnetic resonance spectrum of sulfmyoglobin cyanide was studied at 400 MHz. The position of a methyl-group resonance at low field is consistent with a chlorin-like structure for the prosthetic group. The proton NMR spectrum of the cyanide derivative of the purified prosthetic group which decomposes upon extraction from the protein was found to be the same as that of the cyanide derivative of the prosthetic group extracted from myoglobin and a sample prepared from hemin-Cl.

Correlations among parameters that describe low-spin ferric heme complexes

The g values from low-spin ferric hemes can be related through the t2g hole model to rhombic (V/lambda) and tetragonal (delta/lambda) ligand field components and to the lowest Kramer's doublet energy (E/lambda). The latter is also a measure of unpaired electron sharing among the iron 3d (t2g) orbitals. For a series of ligands (X), there is a monotonic increase in myoglobin complex (Mb . X) [E/lambda] values with nonheme hexacoordinate metal complex (M . X6) [eg-t2gPg] orbital separations. As the aqueous solution pKa values of the sulfurous or nitrogenous ligands in model heme complexes increase, values of V/lambda and delta/lambda increase linearly, but those of [E/lambda] decrease linearly. The greater the electron-acceptor ability of the ligand, as suggested by its position in the spectrochemical series or its pKa, the more the unpaired electron sharing among the heme t2g orbitals increases. The rate of change of [E/lambda] with V/lambda and the pKa is different with sulfurous and nitrogenous ligands, and the magnitude of both rates increases with two sulfurs less than sulfur and nitrogen less than two nitrogens bound to the heme. The maximum magnitude of this rate with V/lambda for cytochrome P-450 is four times less than that for myoglobin, which may explain, in part, the differences in ligand binding between these two hemeproteins. The perturbation of [E/lambda], V/lambda, and delta/lambda induced by strain of iron-ligand bonds is quantitated for several hemeproteins and heme models. In addition, energy level comparisons suggest that the largest-magnitude g value falls approximately along the iron-chlorin ring normal. This suggestion implies that the electron distribution of the iron at the catalytic sites of cytochrome P-450 and certain chlorin-containing enzymes is in some way similar, but distinct from that at the transport site of myoglobin.

A comparison between the ease of haemoglobin oxidation and modification by sulphide

The haemoglobin purified from a wide range of species undergoes facile sulphaemoglobin formation as well as oxidation. Oxidation by either anions such as azide or organic electron transfer reagents shows similar facility. Facile oxidation of a particular haemoglobin is associated with protection against sulphaemoglobin formation. Oxidation and sulphaemoglobin formation in some instances occur via competing electron transfer reactions.