title: An improved cathepsin-D substrate and assay procedure.
abstract: Ten analogs of the peptide A-Phe(NO2)-Phe-Val-Leu-B were synthesized and tested as substrates for cathepsin D and pepsin. The best substrate found for cathepsin D, Phe-Ala-Ala-Phe(NO2)-Phe-Val-Leu-OM4P (kcat = 2.9 s-1; Km = 7.1 microM), has the largest kcat/Km value (408 mM-1 s-1) reported to date for this enzyme. The effect of peptide structure on solubility and kinetic parameters is discussed. The peptide provides a useful new substrate for continuous assay of cathepsin D.
mesh_terms: D002402:Cathepsin D; D002403:Cathepsins / Q000032:analysis*; D007700:Kinetics; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000378:metabolism; D012995:Solubility; D013379:Substrate Specificity
chemical_list: D009842:Oligopeptides; D002403:Cathepsins; D002402:Cathepsin D