1. Specificity of pancreatic elastase with tripeptidyl-p-nitroanilide substrates
G C Szabó, M Pozsgay, R Gáspár, P Elödi Acta Biochim Biophys Acad Sci Hung. 1980;15(4):263-763.
1. The kinetic properties of pancreatic elastase (E.C. 3.4.21.11) were investigated with 33 tripeptidyl-p-nitroanilide substrates, and the Km, kcat and kcat/Km values were determined. 2. The individual contributions of the substrate side chains to the kinetic constants were evaluated by regression analysis. As a result of the additivity of the contributions, the kinetic parameters of any substrate constructed from the amino acid investigated can be predicted. 3. Suc-D-Phe-Pro-Ala-pNA was the best substrate, as far as the Km (Michaelis constant) is concerned. The compound was synthesized and assayed. An excellent correlation was observed between its calculated (14 microM) and experimentally determined (15 microM) Km values. The aldehyde derivatives of this substrate is a competitive inhibitor of elastase (Ki = 0.6 mM). 4. The contribution values of the best substrates permitted us to characterize the topography of subsites involved in the formation of the enzyme-substrate complex. This, in turn, led us to the conclusion that the S3-P3 interaction is relatively less important in the binding of good substrates.
3. Study of the specificity of thrombin with tripeptidyl-p-nitroanilide substrates
M Pozsgay, G Szabó, S Bajusz, R Simonsson, R Gáspár, P Elödi Eur J Biochem. 1981 Apr;115(3):491-5. doi: 10.1111/j.1432-1033.1981.tb06229.x.
The kinetic behaviour of human thrombin has been studied with 26 tripeptidyl-p-nitroanilide substrates protected at the N terminus and with 9 unprotected ones. By the regression analysis of experimentally determined 1/Km, kcat and kcat/Km values the individual contribution of each side chain of the various substrates to the kinetic parameters was calculated. The contributions to the kinetic parameters of the best substrates provide information about the structure of the binding site. The interaction of subsites S1 and P1, which determines primary specificity, proved to be marginal on the basis of contribution values, though it depends upon this contact whether the substrate is hydrolyzed at all. At subsite S2 proline appeared to be favourable. Subsite S3 plays an important role in efficiency. The best parameters were obtained here with the D configurations of bulky amino acid residues. The aromatic protecting groups applied did not improve the properties of substrates. BZDPhe-Pro-Arg-Nan was predicted by calculation to be better than the protected substrates assayed. The compound was synthesized and tested. Its experimentally determined 1/Km, 55.1 mM-1, was in good agreement with 50.9 mM-1 found by calculation.
