Influence of dinitroglycerol and nitroethyleneglycol lipid derivatives on spectral parameters of human hemoglobin.

The interaction of organic nitrates (nitroethyleneglycol, dinitroglycerol, and their esters with arachidonic acid) with oxyhemoglobin and methemoglobin has been studied. Addition of nitroethyleneglycol and dinitroglycerol to oxyhemoglobin is accompanied by a modest but significant increase in oxidation rate of the heme protein to the high-spin ferri-form--methemoglobin. Arachidonoylglycerol dinitrate exerts a similar but more pronounced effect on hemoglobin: a molar excess of this dinitrate induces the transformation of a significant portion of oxyhemoglobin to methemoglobin, whereas arachidonoylnitroethyleneglycol is inactive. Arachidonoylglycerol dinitrate also induces changes in the spectral characteristics of methemoglobin; this may be due to disintegration of the methemoglobin with the loss of heme. The data demonstrate that some organic nitrates can interact with hemoglobin; this should be taken into account when using the oxyhemoglobin technique for measuring nitric oxide generation from these compounds.

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.

Hemoglobin conversion to hemichrome under the influence of fatty acids.

The effect of free fatty acids on the process of hemoglobin conversion and lipid peroxidation has been studied in model systems and erythrocytes. It has been found that methemoglobin and oxyhemoglobin are converted to the low spin oxidized form, namely, reversible hemichrome under the action of fatty acids. In the case of oxyhemoglobin, an increase in the level of active oxygen forms is observed in the system which initiates the formation of primary and secondary lipid peroxidation products. Incubation of erythrocytes with free fatty acids causes the formation of Heinz bodies and is accompanied by an increase of the lipid peroxidation level.