General method for exact evaluation of parameters of the elementary steps of coupled reactions. Invariant analysis.

A general method has been devised for the exact evaluation of the rate constants of the elementary steps of a system consisting of any number of coupled reactions. The method is independent of the structure of the network of coupled steps. The precision of the data evaluation is solely dependent on the quality of the detection unit. The application of the method is illustrated with data collected for the binding of the competitive inhibitor proflavine to chymotrypsin under such conditions that five states of the enzyme are required to interpret the results. In the absence of a substance possessing the binding specificity, the enzyme is present as an equilibrium between an active and an inactive conformer. The latter prevails. The binding of the specific inhibitor releases a slow proton transfer from the medium to the alpha-amino group of Ile-16. Subsequently, the enzyme-inhibitor (or enzyme-substrate) complex re-arranges to the catalytically active form, which is retained until the supply of specific substrate is exhausted. The control features described are general, but are particularly conspicuous under the special environmental conditions used here. A comparison between data for alpha- and delta-forms of chymotrypsin showed that the chain ends of the former impeded the substrate binding and that the activity controlling conformational change occurred in the interior of the enzyme molecule.