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A novel chain of basement membrane-associated collagen as revealed by biochemical and immunohistochemical characterizations of the epitope recognized by a monoclonal antibody against human placenta basement membrane collagen.

Biochemical and immunohistochemical characterizations of the epitope recognized by a monoclonal antibody, JK-132, originally produced against human type IV collagen showed that it was distinct from the previously reported monoclonal antibody, JK-199 (Kino et al, J Biochem 1988, 103:829-835). The bound fraction of a crude pepsin extract of human placenta on JK-132 antibody-coupled resin showed close similarity to type IV collagen in a triple-helical conformation in terms of the amino acid composition and circular dichroism spectrum. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of the fraction showed six peptide bands with molecular weights of 50,000 or below, both before and after reduction. Four of the peptides reacted with JK-132 on immunoelectroblotting, but none reacted with JK-199. JK-132 reacted with two additional bands with molecular weights of 100,000 and 120,000, which were not visible on direct staining with Coomassie Brilliant Blue R-250. Two peptides (molecular weights 40,000 and 15,000) bound on a JK-199 antibody affinity column were sequenced, and both contained the same amino-terminal sequences as alpha 1(IV) chain. Conversely the sequences of three of the peptides (molecular weights 50,000, 32,000, and 23,000) eluted from a JK-132 antibody affinity column did not match either the alpha 1(IV) or the alpha 2(IV) sequence reported. Immunohistochemically, JK-132 reacted strongly with basement membranes of blood capillaries in skeletal muscle tissues but not with the basement membranes of muscle fibers in frozen sections of periodate-lysine-paraformaldehyde-fixed tissue, suggesting heterogeneity or tissue specificity of basement membrane collagen. By immunoelectron microscopy, the reaction products were found on the basal laminae of endothelium and of smooth muscle cells around blood vessels. These findings suggest the presence of a new collagen chain associated with basal laminae.