A fundamental task of proteins is to act as enzymes:catalysts that increase the rate of virtually all the chemical reactions withitin cells.They are high ly selective，accelerating both the rate and specificity of metabolic reactions，from the digestion of food to the synthesis of DNA。Most enzymes are proteins， although some catalytic RNA molecules have been identified as well.Cells contain thousands of different enzymes， and their activities determine which of the many possible chemical reactions actually take place within the cell.The binding of a substrate to the active site of an enzyme is a very specific interaction.Once a substrate is bound to the active site of an enzyme， multiple mechanism can accelerate its conversion to the product of the reaction.Examples of enzymatic conversions of substrates include peptide bond formation or cleavage，hydrolysisand condensation，oxidation and reduction单击功能区上，phosphoration单击功能区上，and many more.In addition to binding their substrates，the active sites of many enzymes bind other ions or small molecules that participate in catalysis.These molecules are called co-enzymes and/or co-factors.In contrast to substrates，coenzymes are not irreversibly altered by the reactions in which they are involved.While most enzymes move freely（intra-and extracellular）within the organism，many enzymes are anchored to either membranes orreceptors[1].The Axon Ligands™，™在线路上，在线路上，在线路上，在线路上，在线路上Nomenclature Committee of the International Union of Biochemistry and Molecular Biology单击功能区上2。