CHROMOGENIC SUBSTRATES UNIVERSITY | SELECTIVITY TABLES
What is a chromogenic Substrate?
Specificity and Selectivity
Substrates in Practice
Protein Concentrations in Plasma
Theoretical Basis for Calculation
International Units and Enzyme Activity
The selectivity data of the table have been compiled to permit the investigator to understand how a contaminating enzyme would influence the enzyme-substrate reaction under study. Another way of expressing this is to say that the table shows the relative reactivities of two or more enzymes on one particular substrate. The table should be read horizontally. Each row represents the reactivity of a substrate designated for use with a particular enzyme, indicated to the left, relative to other relevant enzymes.
Example: The set of data in the top row shows the relative reactivity of the thrombin substrate S-2238 with various enzymes. All the experiments were performed using the same buffer, i.e. the one most appropriate for the reaction between thrombin and chromogenic substrate S-2238. In addition, the substrate concentration was always the same, or 2 x Km for the reaction of chromogenic substrate S-2238 with thrombin. The concentrations of the different enzymes are given in Table 2 and are related to the plasma concentration of the corresponding zymogen. The reactivity of chromogenic substrate S-2238 with thrombin, measured as the time-dependent increase in absorbance (DA/min), is given the value 100% (the actual value of DA/min is given in brackets). The reactivities of chromogenic substrate S-2238 with the enzymes FXa, FXIa, APC, plasmin, single chain t-PA, plasma kallikrein, and C1s have then been related to the reactivity of chromogenic substrate S-2238 with thrombin, and proved to be 5, 5, 40, 5, 5, 60, and 2%, respectively.
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