摘要：

The reaction of heme or hematin with a number of nitrogenous ligands to form ferrihemochromes and ferrohemochromes has been studied spectrophotometrically. The following substances formed both ferri- and ferrohemochromes: pyridine, imidazole, histidine, N-methylhistidine, histidine ethyl ester, leucine methyl and ethyl esters, lysine, lysine ethyl ester, glycine ethyl and butyl esters, phenylalanine, phenylalanine ethyl ester, tryptophan, and S-ethyl cysteine. The following substances formed ferrohemochromes, but not ferrihemochromes: nicotinic acid, nicotinic acid methyl ester, nicotinamide, cysteine ethyl ester, tyrosine, thiohistidine, arginine, leucylleucine, leucylleucylleucine, poly-L-lysine, poly-L-proline, trypsin, casein, ovalbumin, pyrimidine, thiamine. Under the conditions used, neither ferri- nor ferrohemochromes were formed by glycine, glycylglycine, glycylglycylglycine, glycylproline, glycylleucine, alanine, proline, hydroxyproline, N-acetyl proline, leucinamide, betaine, creatinine, creatine, glutathione, α-aminobutyric acid, valine, serine, aspartic acid, asparagine, glutamic acid, δ-amino valeric acid, α-aminovaleric acid, citrulline, cysteine, poly-L-glutamic acid, poly-L-aspartic acid, and polysarcosine. A wide difference in the reactivity of the various ligands with heme or hematin was noted. The esters of α-amino and other acids were considerably more reactive than the free acids. Polypeptides of basic amino acids were more reactive than the monomeric residues. Increasing electronegativity of the ligand apparently enhances reactivity, provided steric factors do not prevail. Shifts in absorption maxima during ferrohemochrome formation and indications of a two-step association curve for certain ligands were noted. However, first-order reaction kinetics were observed, with rates of formation of both ferri- and ferrohemochromes being greatly influenced by pH and ligand concentration. Variations in pH had marked effects on reactivity; ferrihemochromes were formed more readily at neutral pH, and ferrohemochromes at alkaline pH values.

展开