Localization of a liver transglutaminase and a large molecular weight transglutaminase substrate to a distinct plasma membrane domain

Abstract

Rat liver plasma membranes contain transglutaminase activity and a large molecular weight protein aggregate that serves as a substrate for this enzyme (Slife, C.W., Dorsett, M.D., Bouquett, G.T., Register, A., Taylor, E., and Conroy, S. (1985) Arch. Biochem. Biophys. 241, 329-336; Slife, C.W., Dorsett, M.D., and Tillotson, M.L. (1986) J. Biol. Chem. 261, 3451-3456). When purified plasma membranes were sonicated and the different plasma membrane domains were separated by sedimentation through a linear sucrose gradient, virtually all of the transglutaminase activity and the large molecular weight transglutaminase substrate were associated with membrane fragments which migrated to a very dense region of the gradient (1.18 g/cm3). The bile canalicular markers, 5'-nucleotidase and HA-4 antigen, were predominantly found at 1.11 g/cm3, while most of the sinusoidal/lateral marker, CE-9 antigen, was detected at 1.14 g/cm3. Smooth membrane vesicles were observed chiefly at the lighter densities upon morphological analysis, while many filament-bearing, plasma membrane segments and junctional complexes were contained in the heavy transglutaminase fractions. These data show that the plasma membrane transglutaminase and the large molecular weight transglutaminase substrate are associated with a distinct region of the plasma membrane.