Functional properties of the glycosylated minor hemoglobins A 1a-1, A 1a-2 and A 1b. EPR evidence for increased stability of the low affinity quaternary structure and decreased susceptibility to organic phosphate

Abstract

Electron paramagnetic resonance (EPR) spectra of the glycosylated minor hemoglobins A 1a-1, A 1a-2, A 1b and A 1c and the major hemoglobin A 0 in the nitrosyl form have been obtained in the absence and presence of inositol hexaphosphate. In the absence of inositol hexaphosphate, nitrosyl hemoglobins A 1a-1, A 1a-2 and A 1b exhibited a triplet hyperfine structure centered at g = 2.009 which has been shown to be diagnostic of the low affinity (T) quaternary structure. Addition of inositol hexaphosphate to nitrosyl hemoglobins A 0, A 1c, A 1b and A 1a-2 developed a triplet hyperfine structure of the EPR spectra but the magnitude of the hyperfine was decreased in the order of hemoglobins A 0, A 1c, A 1b and A 1a-2. However, inositol hexaphosphate had essentially no effect on the EPR spectrum of nitrosyl hemoglobin A 1a-1. The present results account qualitatively for the oxygen binding properties of these glycosylated minor hemoglobins in the framework of a two-state allosteric model.