This research is designed to determine the structure of the enzyme proline endopeptidase, an ubiquitous cell constituent. The enzyme plays a unique role in the breakdown of proteins due to the special feature of the propyl residues which have the properties of breaking alpha helices. One form of this enzyme is membrane bound and accumulates in synaptosomes isolated from vertebrate brain. It is possible, therefore, that the enzyme has a particular role in protein breakdown in the nervous tissue. The goals of this project are as follows: 1) to determine the structure of the enzyme through isolation and sequence analysis; 2) to identify the specific residues which are critical for enzymatic activity and 3) determine which factors are involved in the heath-mediated conversion of the enzyme in an inactive form.