EVIDENCE FOR THE PRESENCE OF THE PLASMA-MEMBRANE COAT IN THE MEMBRANE-FRACTION ISOLATED FROM CHARA-GYMNOPHYLLA

Previous biochemical and microscopic studies on characean plasma membr anes have indicated the presence of a specific proteoglycan substructu re: the 'plasma membrane coat'. This internal protein contamination co uld have given rise to the previously reported relatively low ATPase-s pecific activity in the Chara gymnophylla plasma membrane fraction. Th us, in order to characterize the plasma membrane fraction from C. gymn ophylla obtained by separation on two-phase polymer systems, a simple IR method was employed. Comparing the relative integrated intensities for amide I and C=O bands, an unusually high protein to lipid ratio wa s obtained (about 80-20%, w/w). The IR spectra also revealed a signifi cant contribution of hydrophylic components which indicated the presen ce of glycoside groups. A high content of proteins and glycoside group s 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 plasm a membrane fraction, possibly associated with the subcellular structur e of the plasma membrane coat, which could be responsible for high pro tein/lipid ratio in plasma membrane fractions.