Subzero temperature study of the inner mitochondrial membrane and related phospholipid membrane systems with the fluorescent probe, trans-parinaric acid

The fluorescence intensity of trans-parinaric acid as a function of the temperature indicates a phase transition in bovine heart mitochondrial inner membranes below 0°C. The comparison of the dye fluorescence intensity in intact inner mitochondrial membranes and in vesicles from extracted phospholipids of mitochondria revealed a similar intensity increase with decreasing temperature. A synthetic phospholipid system of dioleoyl phosphatidylcholine was investigated because of its low phase transition temperature and showed a very definite intensity change at ?25°C. trans-Parinaric acid in membrane systems probes an environment of intermediate polarity; this was found from the excitation and emission spectra and from fluorescence decay.