Reconstitution of purified dipeptidyl peptidase IV. A comparison with aminopeptidase N with respect to morphology and influence of anchoring peptide on function.

The pig small intestinal dipeptidyl peptidase IV was asymmetrically integrated into egg phosphatidylcholine and microvillar lipid vesicles prepared by a beta-octylglucoside dialysis method. The enzyme molecules appeared dumbell-shaped ((11.0-11.5) X (5.0-5.5)nm) and were separated from the liposomal membrane by a stain-filled gap of about 2.5 nm, representing the 'junctional segment'. The influence of lipid bilayer and detergents on the kinetic parameters of amphiphilic and hydrophilic forms of aminopeptidase N and dipeptidyl peptidase IV was studied. Since the lipid bilayer and detergents, which interact only with the anchoring root, had no crucial effect on the kinetic parameters of the different forms of the enzymes, it is concluded that the anchoring roots exert little effect on the catalytic domain of the stalked integral membrane proteins.