How do Km and Vmax characterize an enzyme – catalyzed reaction?
Enzymes are proteins that catalyse biochemical reactions, without undergoing any changes in themselves, and all reactions will have a speed or rate at which they occur. Some reactions will be very fast because there is intrinsic energy within the reactant, or there is lots of either enzyme or reactant. Conversely some will be slower. The rate is often termed the Velocity (Vo) measured in micromole/minute. This is fastest when the substrate has not yet been converted into product or because the the enzyme may be controlled in its activity by negative inhibition by the product and/or the the product will fuel the reverse reaction. A graph of product formed against time would show a curve going up and stopping, as finally the enzyme runs out of substrate. The tangent of the curve would be Vo. There are two standards of enzyme activity – U the enzyme unit and the Katal (Kat) – 1 micromole substrate formed/min and the activity which raises the rate of a reaction by one mole/second respectiv
