ABSTRACT
Basement membranes lie immediately adjacent to the plasma membranes of cells and the component macromolecules of basement membranes appear to function in concert with some molecular components of the plasma membrane; thus, it is appropriate that basement membranes be included in a review of cell membranes. Alterations in basement membranes have been observed in a number of diseases, particularly diabetes mellitus. Basement membranes are ubiquitous extracellular structures that are composed of several macromolecules arranged in a highly organized complex. Collagen was first identified as a component of basement membranes in the early 1950s. Since that time, there has been considerable disagreement as to the number and biochemical nature of collagenous components. Several reports of glycoproteins that are associated with basement membranes or the extracellular matrix are too limited in scope to determine whether these are laminin or entactin or represent additional basement membrane glycoproteins.
