Isolation and characterization of pepsin fragments of laminin from human placental and renal basement membranes

The presence of laminin in authentic basement membranes was examined at the level of a large pepsin-resistant fragment P1. This strongly antigenic fragment has been recently isolated from a mouse tumour basement membrane. By using antibodies to mouse laminin P1 for identification it was possible to isolate a homologous fragment P1 (Mr about 250 000) and a related component Pa (Mr about 70 000--90 000) from pepsin digests of human placenta and kidney. The fragments were in half-cystine (90--130 residues/1000) and carbohydrate and showed strong binding to concanavalin A. Reduction of disulphide bonds produced several smaller peptide chains, indicating a complex pepsin cleavage. Immunological assays demonstrated partial antigenic identity between laminin fragments obtained from mouse and human tissue, and suggested that fragment Pa may originate from a protein not completely identical with laminin. The results showed that laminin is an abundant component of tissue rich in basement membranes, which has been previously suggested by immunohistological studies.