The proposed research aims are firstly to isolate and characterize several brush border membrane peptide hydrolases with different substrate specificity. Purification of these enzymes will be achieved by the use of various chromatographic methods. When purification of the enzymes is achieved, a detailed examination of the kinetic properties of these enzymes and of factors which affect the enzyme activity will be performed to elucidate the mechanisms by which these enzymes are regulated. A second aim of the proposed research is to examine the spatial relationships between these brush border membrane peptidases and other constituents of the brush border membranes. These will be carried out by the physicochemical study of enzyme molecules and the method of lactoperoxidase catalyzed iodination of the surface proteins of the intact cells compared to those of the isolated surface membranes. Furthermore, the kinetics of peptide transport and its relationship to hydrolysis of peptides consisting of different amino acids and of different chain lengths will be studied by both in vitro and in vivo methods in order to elucidate the functional significance of the brush border peptide hydrolases.