The Application and Usefulness of the Ratio kcat/KM

The ratio of two important constituents in enzyme action, kcat and KM, has become of value and provides insight into enzymatic mechanisms and the functional effects of enzyme mutations. It is timely to examine how this ratio is used and where it can be effectively applied. It has been called on some occasions the “specificity constant” and on other occasions, the “performance constant,” and it is of interest to examine which then is the most accurate and useful way to utilize this ratio.