A study of the ultrastructural organization of cytochromec-phospholipid membranes as revealed by various experimental treatments

Summary Two different types of cytochromec-phospholipid model membranes have been investigated by electron-microscopy. The preservation of the lamellar structure of the cytochromec plus phospholipid-water system after extraction of 88% phospholipids with aqueous acetone followed by only aldehyde fixation is revealed.Pronase digestion of this type of model membrane leads to removal of 80% of the protein and loss of ordered structures as revealed by aldehyde post-fixation.It is shown that the hydrated isooctane-soluble cytochromec-phospholipid complex retained the lamellar structures after extraction of 75% phospholipids followed by separate aldehyde and osmium tetroxide fixations. Pronase treatment of this type of model membrane leads to removal of 25 to 30% of the protein. After aldehyde fixation of these pronase-treated samples the triple-layered structures are preserved.The structural integrity of both types of model membranes after organic extractions with aldehyde pre- or post-fixation is thought to be the result of cross-linkage of the protein by aldehyde polymers on both surfaces and through lipid bilayers. Possible localization of cytochromec in investigated model membranes is discussed.