The purification of plasma membranes from WI-38 fibroblasts: effects of ageing on their composition.

A three-step method for the purification of plasma membranes from WI-38 fibroblasts was developed thus allowing the recovery of 36--44% of the plasma membrane. Except in the case of galactosyltransferase, the activity of the contaminating enzymes was very low. Morphological observations confirm the presence of a homogeneous population of vesicles. Preparations obtained from young and old cell cultures were compared for their enzymatic and protein contents. With ageing the activity of 5-nucleotidase significantly increases whereas that of alkaline phosphodiesterase I decreases. Out of the 26 components detected after sodium dodecyl sulphate polyacrylamide gel electrophoresis, four decreased but only one increased. Cellular ageing seems to fulfil a specific and localized effect on the plasma membrane.