Enzyme

Enzymes act as specific catalysts. That is to say each enzyme accelerates one or more specific chemical reactions without affecting the final equilibrium concentrations of reactants and products. In thermodynamic language, enzymes reduce the activation energy of a reaction but do not affect the free energy change of the overall reaction. Many enzymes are so effective that they will catalyse intracellular reactions which are too slow to be observed at all under comparable conditions in the absence of enzyme catalysis. Enzymes are often highly specific, both for the molecules they will accept as substrates and for the precise chemical changes that they will catalyse, and the presence of active enzymes is essential to form most of the molecules in the cell.

Two important enzyme parameters in a simple enzyme catalysed reaction are the Michaelis-Menten constant (K_m) and the maximum reaction velocity (V_max).