Conversion of hemoglobin to hemichrome by lysophospholipids

The interaction of lysophospholipids with human oxy- and methemoglobin was studied. Anionic (acidic) lysophospholipids (lysophosphatidylserine, lysophosphatidylinositol, lysophosphatidylethanol, and lysophosphatidic acid) are potent effectors inducing the conversion of both forms of hemoglobin into hemichrome. Zwitterionic lysophospholipids (lysophosphatidylcholine, lysophosphatidylethanolamine, and lysosphingomyelin) did not influence oxyhemoglobin conversion, whereas methemoglobin conversion into hemichrome required much higher concentrations of these lysophospholipids compared to anionic lysophospholipids. Neutralization of negative charge on phosphate group of acidic lysophospholipids by Ca2+ was accompanied by partial or complete loss of their effector properties. The process of hemoglobin conversion to hemichrome is characterized by two isobestic points in the absorption spectra, indicating lack of stable intermediates. The present results are discussed in terms of the biological sense of the asymmetric distribution of phospholipids in the erythrocyte membrane.