Localization of intestinal sucrase-isomaltase complex on the microvillous membrane by electron microscopy using nonlabeled antibodies.
Microvillous vesicles isolated from rabbit small intestine showed a trilaminar membrane with a rather smooth surface, which was apparently not affected by papain solubilizing sucrase-isomaltase complex or by trypsin unable to solubilize it. When microvilous vesicles or trysinized ones were incubated with immunoglobulin G against the sucrase-isomaltase complex or monovalent fragments therefrom, an apparently continuous electron-opaque layer approximately 180 A in width appeared around the external surface of vesicles. Such a layer was not formed on papainized vesicles. Microvillous vesicles and trypsinized ones negatively stained with phosphotungate showed a great number of particles protruding approximately 150 A from the membrane surface, but papainized vesicles did not. The particles existed close to one another and appeared to form a particulate layer 150 A in width on the surface. The antibodies, whether they were divalent or monovalent, increased the width of the layer to approximately 200 A and obscured the fine particulate structure of intact and trypsinized vesicles. Papainized vesicles retained their smooth surface upon interaction with antibodies. These results, together with those with the Triton-solubilized sucrase- isomaltase complex (Nishi and Takesue, 1978), J. Ultra-struct. Res., 62:1- 12), indicate not only that sucrase-isomaltase complexes are located close to one another on the membrane, but also that they or at least their protein portions protrude approximately 150 A from the surface of the trilaminar membrane.
D000937:Antigen-Antibody Reactions; D002462:Cell Membrane / Q000201:enzymology*; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007421:Intestine, Small / Q000201:enzymology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008871:Microvilli / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000032:analysis*; D012430:Ruthenium Red; D013394:Sucrase-Isomaltase Complex / Q000032:analysis* / Q000276:immunology
D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D009097:Multienzyme Complexes; D012430:Ruthenium Red; D013394:Sucrase-Isomaltase Complex