A catalyst increases the rate of the chemical reaction by making available a new low energy pathway for the conversion of reactants to products. It increases the rate of forward and reverse reactions that pass through the same transition state and does not affect the equilibrium composition of a reaction mixture. Therefore, the value of the equilibrium constant is not changed in the presence of a catalyst . Enzymes are biological catalysts that catalyse biochemical reactions . Non-protein constituents called co-factors (which include coenzymes) bind to the enzyme to make it catalytically active . A catalyst generally does not initiate a reaction but only alters the rate of a spontaneous reaction.