German: Enzym, Ferment
An enzyme is a biochemical catalyst that helps to cleave or otherwise modify a substrate. The enzyme facilitates the necessary reaction by reducing the activation energy, which always has to be overcome for metabolism to take place at all. The enzyme participates in the biochemical reaction; even forms a temporary compound (the enzyme-substrate complex) with the substances to be converted, but remains unaltered by the reaction.
Enzymes are proteins by their chemical nature. Responsible for the catalytic efficiency is the so-called active site, which consists of specially folded parts of the polypeptide chain or reactive non-protein elements of the enzyme molecule. A special hollow structure in the enzyme enables the active site to make contact with a suitable substrate.
The protein portion is responsible for the substrate specificity and for the action specificity (reaction specificity) of an enzyme, i.e. it determines which substances are actually catalyzed and which of the numerous possible reactions the substrate molecule is to take.
The enzyme activity, one of the parameters of enzyme kinetics, depends on exterior factors. A rise in temperature may increase the speed of an enzymatic reaction, but only if the enzyme proteins are not denatured by the higher temperature. Changes in pH value can also affect enzyme activity.
Hundreds of different enzymes are active in our body. If one enzyme is missing, or for instance inactive through vitamin deficiency, severe metabolic disorders can occur. Enzymes are also required by industrial production. Lipase, a fat-cleaving enzyme, is added to detergents to enhance their cleaning performance. Enzymes are also used in the production of some medicines and insecticides. The laboratory enzyme plays a part in cheese production, an enzyme which is extracted from the stomach of calves. Today, many enzymes can be produced with genetically modified microorganisms. The name of an enzyme mostly ends with the syllable -ase, e.g. lipase, amylase, and proteinase. Thus, enzymes are often named after their substrates. But they can also be named after the process which they catalyze. Some exceptions from the rule are the protein-cleaving enzymes trypsin and chymotrypsin from the pancreas and pepsin, which is active in the stomach; these enzymes have kept their traditional trivial names.
Systematics By international convention, enzymes can be classified into six groups according to the reactions that are catalyzed by them; each of them is ascribed an EC number ""(Enzymes Commission)"": Â·
distinguishes four forms of enzyme inhibition:
The substrate and the inhibitor have similar (not identical) structures. The substrate competes with the inhibitor for the active site. The inhibitor cannot be converted and thereby stops the work of the enzyme. The enzyme remains inhibited only with a sufficiently high inhibitor concentration. If the inhibitor concentration decreases and the substrate concentration rises, the enzyme can once again cleave the substrate.
The inhibitor (mostly a heavy metal ion) and the substrate bind to differend sites of the enzyme for this reason there is no competition between substrate and inhibitor. In Non-competitive inhibition enzyme-inhibition complexes and enzyme-substrate-inhibitior complexes can be formed. In competitive inhibition enzyme-substrate-inhibitor complexes cannot be formed.
Uncompetitive inhibitors just bind to enzyme-substrate complex, never to free enzymes. In uncompetitive inhibition enzyme-inhibitor complexes cannot be formed.
In this form of inhibition, the inhibitor becomes active at another site of the enzyme, the allosteric site. It binds there reversibly and changes the form of the active site, so that the substrate does not fit the enzyme anymore. When the inhibitor is displaced from the enzyme by an increase in substrate concentration, the reaction can continue.
Regulation of enzyme activity means the acceleration or deceleration of an enzymatic reaction. The regulation of enzyme activity includes:
an enzyme acts just upon a single steroisomer of a substrate
an enzyme catalyzes just a single typ of chemical reaction
To comment on this article, please login..