Enzyme Kinetics - Discussion of Kcat or TN

Discussion of Kcat or Turnover Number

In order to understand turnover numbers we have to go back to the basic properties of enzymes. Very small amounts of enzyme, referred to as catalytic amounts , are required for catalysis. One of the basic characteristics of all catalysts, enzymes include d, is that the catalyst must emerge from the reaction unaltered and be able to recycle. This recycling leads to the concept of turnover number (TN). The turnover number is the maximum number of substrate molecules which can be converted to product in a unit of time (usually one second) by a single molecule of enzyme.

Catalase ( ) has one of the highest turnover numbers known, 1x10. That is, each substrate molecule takes only about 1.7x10 sec or 0.1 microsec to be converted to product. On the other hand, lysozyme takes two (2) sec. to convert a substrate molecule to product. Most enzymes have turnover numbers between 1 and 10. This is possible because the catalyst is recycled, and used over and over.

Below is a series of values for , kcat and kcat / which should give you some idea of the ranges which are found.

The Thomas Jefferson University web site, its contents and programs, is provided for informational and educational purposes only and is not intended as medical advice nor is it intended to create any physician-patient relationship. Please remember that this information should not substitute for a visit or a consultation with a health care provider. The views or opinions expressed in the resources provided do not necessarily reflect those of Thomas Jefferson University, Thomas Jefferson University Hospital, or the Jefferson Health System or staff.

Return to Thomas Jefferson University Home Page