title: Fibronectin is a component of the sodium dodecyl sulfate-insoluble transglutaminase substrate.
abstract: Liver plasma membranes contain a morphologically distinct protein complex which serves as a substrate for the plasma membrane-associated transglutaminase. The complex, which appears as a two-dimensional sheet, is insoluble in sodium dodecyl sulfate and reducing agents and has been named SITS for sodium dodecyl sulfate-insoluble transglutaminase substrate (Tyrrell, D. J., Sale, W. S., and Slife, C. W. (1988) J. Biol. Chem. 263, 1946-1951). Polyclonal antibodies raised against SITS were used to probe for soluble constituents of the matrix. Immunoblots showed that proteins of 230, 35, and 32 kDa reacted with the anti-SITS antiserum when the soluble fraction from a liver homogenate was examined. The 230-kDa protein was identified as fibronectin after observing cross-reactivity of anti-SITS antiserum with authentic fibronectin and cross-reactivity of anti-fibronectin antiserum with the 230-kDa cytosolic protein and purified SITS. Preincubating anti-SITS antiserum with purified fibronectin decreased immunostaining of the 230-kDa cytosolic protein and authentic fibronectin. Immunoblots of the plasma membrane fraction using anti-SITS and anti-fibronectin antisera showed that both antisera reacted with proteins at the top of the stacking gel (SITS) and of 230 kDa. In addition, the anti-SITS antiserum reacted with proteins of 85, 35, and 32 kDa. Immunofluorescence microscopy revealed that the anti-SITS and anti-fibronectin antisera both react with isolated SITS and with the same filamentous structures associated with intact plasma membranes. These studies show that fibronectin is a component of the plasma membrane matrix, SITS. This finding is consistent with the proposed role of this matrix which is to mediate cell-cell adhesion between hepatocytes in the tissue.
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000818:Animals; D005353:Fibronectins / Q000032:analysis*; D005455:Fluorescent Antibody Technique; D007163:Immunosorbent Techniques; D008099:Liver / Q000201:enzymology; D008297:Male; D051381:Rats; D012967:Sodium Dodecyl Sulfate; D012995:Solubility; D011503:Transglutaminases / Q000378:metabolism*
chemical_list: D005353:Fibronectins; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012967:Sodium Dodecyl Sulfate; D011503:Transglutaminases