Evidence for the presence of the plasma membrane coat in the membrane fraction isolated from Chara gymnophylla

Abstract

Previous biochemical and microscopic studies on characean plasma membranes have indicated the presence of a specific proteoglycan substructure: the 'plasma membrane coat'. This internal protein contamination could have given rise to the previously reported relatively low ATPase-specific activity in the Chara gymnophylla plasma membrane fraction. Thus, in order to characterize the plasma membrane fraction from C. gymnophylla obtained by separation on two-phase polymer systems, a simple IR method was employed. Comparing the relative integrated intensities for amide I and CO bands, an unusually high protein to lipid ratio was obtained (about 80-20%, w/w). The IR spectra also revealed a significant contribution of hydrophylic components which indicated the presence of glycoside groups. A high content of proteins and glycoside groups in the plasma membrane fraction pointed to the presence of membrane-bound proteoglycans. Electron microscopy with tannic acid staining has further indicated the presence of proteoglycans in the purified plasma membrane fraction, possibly associated with the subcellular structure of the plasma membrane coat, which could be responsible for high protein/lipid ratio in plasma membrane fractions. © 1995.