Bromothymol blue as a probe for structural changes of model membranes induced by hemoglobin.

The effect of methemoglobin on the structure of model membranes composed of phosphatidylcholine and diphosphatidylglycerol (18 : 1, mol : mol) was studied with the help of pH-indicator dye bromothymol blue. The partition coefficients characterizing the dye binding to methemoglobin or model membranes were derived from the pKaalpha dependences on the protein or phospholipid concentration. The observed character of the dye partitioning in the lipid or lipid-protein systems is interpreted in terms of the traditional electrostatic approach and some modern theories of membrane electrostatics. It is assumed that methemoglobin affects the structural and physicochemical parameters of lipid-water interface.