A protein produced by a living organism capable of catalyzing a chemical reaction Almost all processes in living organisms require some form of enzyme to cause the reactions to occur at a rate sufficient to support life There are a very wide variety of enzymes each specifically catalyzing a different chemical reaction the sum of which cause the bulk of the physiological changes observed as life processes Enzymes like most proteins are synthesized by the protein synthetic mechanism of the living cell at special sites on ribosomes using the genetic information in messenger RNA transcribed from the genetic instructions stored as nuleotide sequences in the DNA or in some viruses the RNA of the genome Some examples of enzymes are pepsin diastase rennet DNA polymerase invertase glucose oxidase protease and ribonuclease There are many other types of enzyme