The objective of our research is to determine the role and regulation of the reaction catalyzed by cholesterol esterase, cholesteryl ester plus water reversibly yields cholesterol plus fatty acid, in the development and regression of atherosclerosis. We will identify the number of distinct cholesterol esterase species in porcine aorta and will purify and characterize each. We will also purify and characterize the effectors of activity which have been indicated. The kinetic and thermodynamic parameters which govern the reaction will be determined as a function of pH, ionic strength, substrate packing density and substrate composition. The experimental system will be comprised of well defined monolayers of substrates at either an air-water or oil-water interface with either pancreatic or aortic cholesterol esterase in an aqueous phase. Such a system will allow the reaction parameters to be determined accurately and reproducibly. Comparison of the data with the physical properties of the lipids measured in monolayers will allow the identification and quantitation of lipid-lipid and lipid-enzyme interactions. The specificities and magnitudes of these interactions coupled with specific measurement of cholesterol esterase levels in aortic tissue will provide a basis for understanding the relationship between the intrinsic physico-chemical properties of aortic lipids and the accumulation of cholesteryl esters in the aorta.