Mouse heart laminin. Purification of the native protein and structural comparison with Engelbreth-Holm-Swarm tumor laminin.

Laminin was selectively extracted from different mouse tissues using EDTA-containing buffer. By immunoblotting with an antiserum raised against mouse Engelbreth-Holm-Swarm (EHS) tumor laminin, such extracts could be shown to contain laminin-like molecules with a low apparent proportion of A chain to B chains. Native laminin was purified from mouse heart tissue and was shown to have an aberrant polypeptide composition as compared to mouse EHS tumor laminin. Most prominently, mouse heart laminin contains an Mr 300,000 polypeptide which is not antigenically related to the A or the B chains. Furthermore, nonreducible polypeptide components were seen with apparent Mr values of 600,000 and 900,000. The Mr 600,000 component contains epitopes shared with both EHS tumor laminin and the Mr 300,000 polypeptide and possibly represents a covalently cross-linked complex of an A or B chain with the Mr 300,000 chain.