What is an enzyme ?
An enzyme is a protein, which acts as a catalyst in a particular chemical reaction in or outside of a cell. The enzyme reaction makes possible or accelerates the reaction without itself being consumed or change in composition. The substance in which the enzyme acts and which is needed for the metabolism or digestive is called the substrate. During the reaction, the enzyme itself momentarily connects with the substrate. This is done for each enzyme in a different way, since each enzyme is specific.
Enzymes found in food, to the extent not (long-term) has been heated. They are also in cells of the organism of the animals, plants, fungi and micro-organisms created. For the build-up of them are needed in a number of cases vitamins.
After the reaction, the enzyme returns to its original state and immediately it can accelerate a reaction. An enzyme "wait" until the molecules that the enzyme "get to work" are accessible. The enzyme then clamps located at a position on the substrate, usually molecules of foods that are dissolved, where that fits and to which it is thus suitable. That portion which is clamped, is detached from the larger whole, after which the enzyme is free again, and may further using the following molecule (part). The place where enzyme and substrate adhere to each other are called the key for the substrate and the lock or active site for the enzyme. When the enzyme to adhere to the substrate, there is an induced fit. Thus, nutrients are broken into small pieces and processed in, the digestive system. Chains of molecules of various kinds, can thus be converted to other simple molecules.
Enzymes are often specific for their substrate, typically an enzyme, but binds to a substrate. However, there are enzymes that can convert a lot of different substrates. Of these, there are a couple for in the liver, for example CYP2D6, an enzyme of the cytochrome P450 enzyme system. Many enzymes are faster and more efficient than hitherto designed by man catalysts. Enzymes are also, therefore, also be used in chemical processes, for example in the food preparation. Without enzymes, metabolic processes would not be possible so that it can be stated that enzymes keep life going.
Co-enzymes
Enzymes can also consist of multiple parts, for example, multiple proteins. In addition, they often have a coenzyme, a smaller component without which the enzyme can not fulfill its function. For example, this may be a metal ion. The co-enzyme acts in a cell, often as a kind of on / off switch. By varying the concentration of the metal ion, the chemical reaction that the enzyme facilitates delayed or accelerated.
Many enzymes will not work without the presence of a co-factor, which is an additional factor which does not consist of protein. That can be an ion of, for example, zinc, manganese, copper, magnesium, iron, potassium or sodium. These are the trace elements in food. The co-factor may also be a small organic molecule, a co-enzyme. Examples are the vitamins B: B1 thiamine, riboflavin B2, as well as ascorbic acid and nicotinamide C. Co-enzymes can be covalently bound strongly to the protein part of the enzyme or very weak. Then, they are only temporarily bound to the enzyme, when it carries out its catalytic function.
Classification of enzymes
Enzymes are named in the process that they catalyze, followed by the ending-ase.
- Oxidase enzymes are enzymes that catalyze oxidation and reduction reactions. These include the enzymes desaturasen, hydrogenasen, oxidasen, hydroxylasen, transhydrogenasen and reductases. Common coenzymes in this group are NAD + and FAD.
- Transferases are enzymes that groepsoverdrachts reactions such as methyl, carboxyl-, amino-acyl-, glycosyl-, or catalyze fosfaatgroepoverdracht. These include trans phosphatases or kinases and the transaminases. At the latter comes the coenzyme pyridoxal phosphate.
- HYDROLASES are enzymes that catalyze hydrolysis reactions. Enzymes from this group include peptidasen, glycosidasen and phosphatases, esterases.
- Lyasen are enzymes that cleavage of C-C, C-O and C-N bonds through catalyze elimination reactions. Enzymes from this group are decarboxylasen and dehydratasen. Used coenzymes are Coenzyme A and thiaminepyrofosfaat.
- Enzymes catalyze → isomerization reactions. This includes racemasen and epimerasen.
- Ligases are enzymes that catalyze the coupling of two substrates with a binding of a carbon atom with another atom is formed, usually with oxygen, nitrogen or sulfur. The necessary energy is often provided by hydrolysis of ATP. This group includes, among other things, elongasen, synthetasen and carboxylasen. Important coenzymes are acetyl Coenzyme A and biotin.
The velocity of an enzymatic reaction, or enzyme kinetics, depends on the temperature, the acidity and the concentration of enzyme and substrate. Concentrations of any co-enzymes or foreign agonists and antagonists may also have an influence on the reaction rate. The enzyme activity can be affected by several factors:
- The temperature
- The acidity
- The enzyme concentration
- The substrate specificity
The spatial structure of proteins changes with the temperature. For example, most enzymes are inactive at low temperatures. Above 50 °, the functioning of the protein is also blocked by denaturation. Each enzyme has at a certain temperature, the so-called optimum temperature, the maximum activity. The activity of enzymes is often expressed in terms of the amount of substrate that can be converted in a certain period. Since enzymes are often the catalyst for a specific conversion, there are so many types of substrate, including very many units.
Each enzyme has an optimal activity at a certain temperature. At a low temperature, most enzymes are not active, because the particles move too slow. At higher temperatures, above 50 ° C, an enzyme can be done by denaturation, the loss of the ternary and quaternary structure, also no longer function. The enzyme activity is maximum around 37 ° C. That's not for nothing that the human body temperature. For example, when we have a fever, reduce our enzyme activity, because our body temperature rises. Conversely, the same goes for hypothermia: the enzyme activity decreases.
Effect of the enzyme concentration
Also, the enzyme concentration has a large influence on the enzyme activity. When an enzyme having a decreasing concentration acting on a substrate, the force is greatest at the highest concentration. That is not to say that enzymes are not active at low concentrations, on the contrary. This also points to the reusability of an enzyme after a chemical reaction.
Enzyme inhibitors
Will the enzyme can exert its effect, then between enzyme and substrate are short and close contact. When the substrate, where the enzyme binds to itself, receives competition of a molecule, which is called "competitive inhibition", whose structure is very similar to that of the substrate, it can inhibit the operation. The competitive molecule binds to the enzyme itself and ensures that the enzyme can not bind to the normal substrate, whereby the reaction is prevented. These substances are capable of inhibiting or stopping processes in the cell. Examples of enzyme inhibitors are some chemical pesticides, such as DDT, which inhibit the activity of key enzymes in the nervous system. Many antibiotics inhibit specific enzymes in bacteria. For example, penicillin blocks the active portion of an enzyme, which use a lot of bacteria in order to build their cell walls.
Other toxins inhibit the enzyme activity in that they attach themselves to a different site of the enzyme, which is called "noncompetitive inhibition", whereby the shape change and the efficacy of the enzyme is prevented. The substrate can no longer bind to bind to the enzyme, because it has undergone a change. There can be no "induced fit" longer take place between the substrate and enzyme.
Allosteric regulation
Many enzymes contain in addition to the active center is also a specific receptor site, which is called allosteric side. Molecules can bind to this location by means of a weak binding, a non-covalent bond, and thus induce a conformational change to the enzyme. The molecules that can bind to the allosteric inhibition as both-side excitation, which is stimulation, effecting the enzyme activity.
Most of the allosteric regulation enzymes consist of two or more polypeptide chains, or subunits. Each subunit has its own active site and the allosteric side is usually between the individual subunits. The binding of a activatormolecule to the allosteric side stabilizes the conformation of the active site. All subunits may conform, if there is one activatormolecule reacts with the allosteric side. The conformational change of one subunit has a direct consequence for the same conformational change in the other subunits: a kind of chain reaction.
Sometimes a activatormolecule and an inhibitor molecule the same in shape in order to compete for the same side of an allosteric enzyme. Some enzymes in catabolic pathways have an allosteric side for both adenosine triphosphate (ATP) as adenosine monophosphate (AMP). These enzymes are inhibited by ATP and activated by AMP. This makes sense, because a very important function of the cell is to regenerate ATP. If the ATP production behind comes to lie, is accumulated and AMP activates the enzyme to the ATP katabolyseren faster again. If the ATP exceeds the demand, the katabolyseren decreases, because the ATP accumulates.