Pig intestinal microvillar maltase-glucoamylase. Structure and membrane insertion.
The NH2-terminal sequence (25 residues) of amphiphilic single polypeptide chain maltase-glucoamylase (EC 3.2.1.20) was determined by gas-phase sequencing. The result indicates that the NH2-terminal segment anchors the enzyme to the microvillar membrane. The single-chain form and the proteolytically processed two-chain form have two distinct active sites differing in heat stability. However, both sites are sensitive to chonduritol B-epoxide and have similar substrate specificity. The amphiphilic single-chain maltase-glucoamylase and the amphiphilic proteolytically processed form were inserted into liposomes and studied by electron microscopy. The results showed that the enzyme is predominantly present as a homodimeric complex in the membrane.
D000595:Amino Acid Sequence; D000818:Animals; D005959:Glucosidases / Q000032:analysis*; D007422:Intestines / Q000648:ultrastructure*; D008081:Liposomes; D008565:Membrane Proteins / Q000032:analysis; D008854:Microscopy, Electron; D008871:Microvilli / Q000201:enzymology*; D008958:Models, Molecular; D013552:Swine; D000520:alpha-Glucosidases / Q000032:analysis*
D008081:Liposomes; D008565:Membrane Proteins; D005959:Glucosidases; D000520:alpha-Glucosidases