text: why the transition metal ion are choosen by the nature in various metallo enzyme?   transition metals in general catalyze an incredible array of reactions, and nature makes full use of these abilities in metalloenzymes. as a result, there are many different purposes for transition metals in proteins.  often the metal center serves as a lewis acid to help catalyze a reaction, as is found in many metalloproteinases.  since metals can be reversibly oxidized and reduced (which is not true of normal amino acids) they play an important role in reduction and oxidation reactions. this is esepecially important for processes like photosynthesis and oxidative phosphorylation.  metal centers are also important for storing certain compounds, such as oxygen. we all rely on hemoglobin and myoglobin for oxygen storeage.  there are many other uses as well, but these are most of the major ones.