The active site of porcine elastase

This paper describes the mapping of the active site of pancreatic porcine elastase, and it includes the size of the site, the stereospecificity and the specificity of its various subsites. The precise size of the active cleft was determined by measuring the kinetic parameters of the hydrolysis of peptide substrates of the type Ala₄LysPheAla, Ala₄LysPheAla₂ and Ala₅LysPheAla₂ (the dash indicates the cleaved bond). Specific local interactions at the various subsites and their stereospecificity were determined by comparative study of the steady-state kinetic parameters of the appropriate group pairs of substrates. Alignment of the substrate Ala₅-Lys-Phe-Ala, and the study of its interactions at the active site of the crystalline enzyme as compared to the enzyme in solution, were achieved by constructing the CPK (space-filling) model of elastase based on its known co-ordinates determined at 2.5 Å resolution.