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

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Abstract
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 tumor basement membrane. By using antibodies to mouse laminin P1 for identification it was possible to isolate a homologous fragment P1 (MW .apprx. 250,000) and a related component Pa (MW .apprx. 70,000-90,000) from pepsin digests of human placenta and kidney. The fragments were rich in half-cystine (90-130 residues/1000) and carbohydrate and showed strong binding to concanavalin A. Reduction of disulfide 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 tissues rich in basement membranes, which has been previously suggested by immunohistological studies.