The proposed research is a study of the structure and function of bovine enterokinase. The properties of the highly purified enzyme will be compared to those of other serine proteinases. We will determine the amino acid sequence of the light chain (the catalytic chain) of the enzyme. The sequence analysis will be performed with a solid-state methodology and will utilize a strategy that minimizes the amount of protein consumed. A selective reduction of the disulfide bonds linking the heavy and light chains will be performed under conditions that maintain the globular structures of the chains. The catalytic properties of the isolated light chain will be investigated; the heavy chain will be tested for regulatory properties. Native enterokinase will be incorporated into synthetic phospholipid vesicles and the properties of the membrane-bound enzyme will be related to those of the free enzyme. Studies will be performed to show that enterokinase is bound in the phospholipid bilayer and that its properties are the same as the naturally occurring enzyme found in the brush border membrane.