title: pH dependence of salt activation of human leukocyte elastase.
abstract: The effects of pH on salt stimulation of the rates of hydrolysis of three substrates by human leukocyte elastase were studied. The enzyme was most active at pH 10.5, 8.0-8.5, and 9.5 for the hydrolyses of fluorescein isothiocyanate-labeled S-carboxymethylated bovine serum albumin (FITC-CM-BSA), succinyl-L-Ala-L-Pro-L-Ala-7-methylcoumaryl-4-amide (Suc-APA-MCA), and succinyl-L-Ala3-p-nitroanilide (Suc-Ala3-pNA), respectively, in the absence of NaCl. The enzyme was activated by 0.5 M NaCl similarly at all pHs tested for the hydrolysis of Suc-Ala3-pNA, but more at neutral and alkaline pH values, respectively, for the hydrolyses of FITC-CM-BSA and Suc-APA-MCA. Thus, in the presence of 0.5 M NaCl, the enzyme was most active at pH 8.0 and 10.0 with FITC-CM-BSA and Suc-APA-MCA, respectively. In contrast, the proteolytic activity of porcine pancreatic elastase was somewhat inhibited by 0.5 M NaCl.
mesh_terms: D004789:Enzyme Activation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007962:Leukocytes / Q000201:enzymology*; D009994:Osmolar Concentration; D010196:Pancreatic Elastase / Q000097:blood*; D012492:Salts; D013379:Substrate Specificity
chemical_list: D012492:Salts; D010196:Pancreatic Elastase