The region on the enzyme where the non-competitive inhibitor binds is known as the allosteric site, these sites are one of the most important ways of regulating enzyme activity. It often contributes to the chemical reaction, sometimes it acts as a source of energy, helping the reaction to occur. Alternatively the co-factor can be a small organic molecule, these are termed coenzymes and are often related to vitamins. Cofactors, like enzymes can be used again and again. Some enzymes have the coenzyme covalently bonded to the them in an almost permanent way, if this occurs the coenzyme is known as a prosthetic group.
Some enzymes can become damaging if they are active in the wrong place.
For example pepsin is capable of destroying body cells, therefore stomach cells manufacture pepsin in an inactive called pepsinogen. The enzyme only becomes active when pepsinogen is exposed to a strong acid, cells lining the stomach are protected by a layer of mucus. If a sequence of reactions must take place in a set order the enzymes are often arranged closely together and in the correct order, to effectively 'hand-on' the product of their reaction. In fact most enzymes in cells are bound to membranes to control their activity. Precise control is achieved by a process known as feedback inhibition.