title: Enzyme inhibition assays using fluorescence correlation spectroscopy: a new algorithm for the derivation of kcat/KM and Ki values at substrate concentrations much lower than the Michaelis constant.
abstract: A new mathematical formalism is deduced which allows for the calculation of the k(cat) over K(M) ratio based on measurements of the enzyme kinetics with substrate concentrations much lower than K(M). The equations are also applied on the action of an inhibitor on enzyme activity yielding the binding constant, K(i), of an inhibitor molecule. For practical evaluation of the new theoretical approach, the enzymatic reaction of CD45 phosphatase was used as a well-characterized model system with known inhibitors for testing the K(i) value determination scheme. The k(cat)/K(M) ratio was calulated to be 4.7 x 10(5) M(-)(1) s(-)(1), the K(i) of the inhibitor molecule PKF52-524 was estimated to be (1-2) x 10(-)(7) M and the association rate of the inhibitor PKF52-524 to CD45 phosphatase was estimated to be 59 M(-)(1) s(-)(1).
authors.affiliation: EVOTEC Analytical Systems GmbH, Max-Planck-Strasse 15a, 40699 Erkrath, Germany, and Novartis Forschungsinstitut, Brunnerstrasse 59, A-1235 Vienna, Austria.
authors.forename: F J
authors.initials: FJ
authors.lastname: Meyer-Almes
authors.forename: M
authors.initials: M
authors.lastname: Auer
mesh_terms: D000465:Algorithms; D001667:Binding, Competitive; D002384:Catalysis; D020134:Catalytic Domain; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D017493:Leukocyte Common Antigens / Q000378:metabolism; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000378:metabolism; D008956:Models, Chemical; D009842:Oligopeptides / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D012235:Rhodamines / Q000378:metabolism; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013379:Substrate Specificity
chemical_list: C114557:5-carboxytetramethylrhodamine succinimidyl ester; D004791:Enzyme Inhibitors; D009842:Oligopeptides; D012235:Rhodamines; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D017493:Leukocyte Common Antigens; D017027:Protein Tyrosine Phosphatases