ABSTRACT
Intestinal aminopeptidase A and aminopeptidase N are respectively responsible for the hydrolysis of acidic and neutral N-terminal residues of synthetic substrates such as p-nitroanilides and of the peptides resulting from protein degradation by pancreatic enzymes. They are among the more abundant hydrolases of the brush border membrane. In the absence of EDTA in an isotonic medium the brush border membrane spontaneously forms vesicles. An improved technique has been devised for the purification of large amounts of these vesicles. Electron micrographs of negative staining and thin sections of this material showed that vesicles are very homogeneous in size. The first type of vesicle preparation has been used for the topological studies of the external components of the membrane. The second type of vesicle preparation is performed; it is easy to trap into vesicles a high molecular weight reagent present in the medium as their formation proceeds.
