<P> Enzymes can couple two or more reactions, so that a thermodynamically favorable reaction can be used to "drive" a thermodynamically unfavourable one so that the combined energy of the products is lower than the substrates . For example, the hydrolysis of ATP is often used to drive other chemical reactions . </P> <P> Enzyme kinetics is the investigation of how enzymes bind substrates and turn them into products . The rate data used in kinetic analyses are commonly obtained from enzyme assays . In 1913 Leonor Michaelis and Maud Leonora Menten proposed a quantitative theory of enzyme kinetics, which is referred to as Michaelis--Menten kinetics . The major contribution of Michaelis and Menten was to think of enzyme reactions in two stages . In the first, the substrate binds reversibly to the enzyme, forming the enzyme - substrate complex . This is sometimes called the Michaelis - Menten complex in their honor . The enzyme then catalyzes the chemical step in the reaction and releases the product . This work was further developed by G.E. Briggs and J.B.S. Haldane, who derived kinetic equations that are still widely used today . </P> <P> Enzyme rates depend on solution conditions and substrate concentration . To find the maximum speed of an enzymatic reaction, the substrate concentration is increased until a constant rate of product formation is seen . This is shown in the saturation curve on the right . Saturation happens because, as substrate concentration increases, more and more of the free enzyme is converted into the substrate - bound ES complex . At the maximum reaction rate (V) of the enzyme, all the enzyme active sites are bound to substrate, and the amount of ES complex is the same as the total amount of enzyme . </P> <P> V is only one of several important kinetic parameters . The amount of substrate needed to achieve a given rate of reaction is also important . This is given by the Michaelis - Menten constant (K), which is the substrate concentration required for an enzyme to reach one - half its maximum reaction rate; generally, each enzyme has a characteristic K for a given substrate . Another useful constant is k, also called the turnover number, which is the number of substrate molecules handled by one active site per second . </P>

What is the end result of enzyme activity