FORMATION OF AN ENZYME-SUBSTRATE COMPLEX IS THE FIRST STEP IN ENZYMATIC CATALYSIS Much of the catalytic power of enzymes comes from their bringing sub- strates together in favorable orientations in enzyme-substrate(Es) com lexes. The substrates are bound to a specific region of the enzyme called the active site. Most enzymes are highly selective in their binding of sub- strates. Indeed the catalytic specificity of enzymes depends in part on the specificity of binding. Furthermore, the activities of some enzymes are controlled at this stage