Optical and Oxygen Binding Properties of Spirographis, Isospirographis, and 2,4-Diformyl Hemoglobins

Abstract

Spirographis (2-formyl-4-vinyldeutero-), isospirographis (Z-vinyl-4-formyldeutero-), and 2,4-diformyldeuterohemins were recombined with human apohemoglobin to form the corresponding holohemoglobins.The two isomer hemoglobins containing monoformyl-monovinyl hemins showed distinct differences not only in the absorption spectra but also in the oxygen binding properties.The absorption maxima of spirographis hemoglobin were shifted toward the longer wavelengths by about 4 nm compared to those of isospirographis hemoglobin.Spirographis hemoglobin showed a considerable cooperativity (n = 1.7) with a psO of 6 mm Hg, in 0.1 M potassium phosphate buffer, pH 7.0, while the other two hemoglobins had 2 to 3 times higher oxygen affinities without showing a significant cooperativity.These results indicate that the two vinyl groups at positions 2 and 4 of the porphyrin ring are functionally nonequivalent.This difference is attributed to the different electron attraction toward the periphery of the porphyrin ring and to the heme-heme interaction.Since the electronic properties of the two isomer hemins before recombination are similar to each other, the different optical and oxygen binding properties of the two isomer hemoglobins must be caused by the interaction with apohemoglobin molecule.Oxygen affinities of hemoglobins can be correlated to the electron-withdrawing effects of heme substituents when these protein factors are normalized.The prosthetic group of hemoproteins lies in a hydrophobic pocket of the protein molecule.The characteristic properties of each hemoprotein may be determined by the nature of interactions between the heme and the protein,The structural relationship of the heme with amino acid residues of hemoglobin has been shown by Perute et al. (1).There are about 60 interactions between atoms of the globin chains which come to within 4 A of