Enzyme is what type of protein

When the cofactor is in place so that it becomes an active enzyme, it is called a holoenzyme. There are two basically different sorts of cofactors. Some are bound tightly to the protein molecule so that they become a part of the enzyme - these are called prosthetic groups. Some are entirely free of the enzyme and attach themselves to the active site alongside the substrate - these are called coenzymes.

Prosthetic groups can be as simple as a single metal ion bound into the enzyme's structure, or may be a more complicated organic molecule which might also contain a metal ion.

The enzymes carbonic anhydrase and catalase are simple examples of the two types. The ideal gas law is easy to remember and apply in solving problems, as long as you get the proper values a.

Carbonic anhydrase is an enzyme which catalyses the conversion of carbon dioxide into hydrogencarbonate ions or the reverse in the cell. If you look this up elsewhere, you will find that biochemists tend to persist in calling hydrogencarbonate by its old name, bicarbonate! In fact, there are a whole family of carbonic anhydrases all based around different proteins, but all of them have a zinc ion bound up in the active site.

In this case, the mechanism is well understood and simple. We'll look at this in some detail, because it is a good illustration of how enzymes work. The zinc ion is bound to the protein chain via three links to separate histidine residues in the chain - shown in pink in the picture of one version of carbonic anhydrase. The zinc is also attached to an -OH group - shown in the picture using red for the oxygen and white for the hydrogen.

If you look at the model of the arrangement around the zinc ion in the picture above, you should at least be able to pick out the ring part of the three molecules. The zinc ion is bound to these histidine rings via dative covalent co-ordinate covalent bonds from lone pairs on the nitrogen atoms. Simplifying the structure around the zinc:. The arrangement of the four groups around the zinc is approximately tetrahedral.

Notice that I have distorted the usual roughly tetrahedral arrangement of electron pairs around the oxygen - that's just to keep the diagram as clear as possible. So that's the structure around the zinc. How does this catalyse the reaction between carbon dioxide and water? A carbon dioxide molecule is held by a nearby part of the active site so that one of the lone pairs on the oxygen is pointing straight at the carbon atom in the middle of the carbon dioxide molecule.

Attaching it to the enzyme also increases the existing polarity of the carbon-oxygen bonds. If you have done any work on organic reaction mechanisms at all, then it is pretty obvious what is going to happen. The lone pair forms a bond with the carbon atom and part of one of the carbon-oxygen bonds breaks and leaves the oxygen atom with a negative charge on it.

The next diagram shows this broken away and replaced with a water molecule from the cell solution. All that now needs to happen to get the catalyst back to where it started is for the water to lose a hydrogen ion. This is transferred by another water molecule to a nearby amino acid residue with a nitrogen in the "R" group - and eventually, by a series of similar transfers, out of the active site completely.

This is a wonderful piece of molecular machinery! At the time, I mentioned the non-protein groups which this contains, shown in pink in the picture. These are heme US: heme groups bound to the protein molecule, and an essential part of the working of the catalase.

The heme group is a good example of a prosthetic group. If it wasn't there, the protein molecule wouldn't work as a catalyst. The heme groups contain an iron III ion bound into a ring molecule - one of a number of related molecules called porphyrins.

The iron is locked into the centre of the porphyrin molecule via dative covalent bonds from four nitrogen atoms in the ring structure. There are various types of porphyrin, so there are various different heme groups. The one we are interested in is called heme B, and a model of the heme B group with the iron III ion in grey at the centre looks like this:. The reaction that catalase carries out is the decomposition of hydrogen peroxide into water and oxygen.

A lot of work has been done on the mechanism for this reaction, but I am only going to give you a simplified version rather than describe it in full. Although it looks fairly simple on the surface, there are a lot of hidden things going on to complicate it. Essentially the reaction happens in two stages and involves the iron changing its oxidation state.

An easy change of oxidation state is one of the main characteristics of transition metals. In the first stage there is a reaction between a hydrogen peroxide molecule and the active site to give:. Changes in temperature and pH have great influence on the intra- and intermolecular bonds that hold the protein part in their secondary and tertiary structures. Examples of cofactors are 1.

Prosthetic group that are permanently bound to the enzyme. Coenzymes, usually vitamins or made from vitamins which are not permanently bound to the enzyme molecule, but combine with the enzyme-substrate complex temporarily. Enzymes require the presence cofactors before their catalytic activity can be exerted.

This entire active complex is referred to as the holoenzyme. Without enzymes, our guts would take weeks to digest our food, our muscles, nerves and bones would not work properly and so on…. Oxidoreductases: All enzymes that catalyse oxido-reductions belong in this class.

The substrate oxidized is regarded as a hydrogen or electron donor. The classification is based on 'donor:acceptor oxidoreductase'. The common name is 'dehydrogenase', wherever this is possible; as an alternative, 'acceptor reductase' can be used.

Classification is difficult in some cases, because of the lack of specificity towards the acceptor. Transferases: Transferases are enzymes that transfer a group, for example, the methyl group or a glycosyl group, from one compound generally regarded as donor to another compound generally regarded as acceptor.

The classification is based on the scheme 'donor:acceptor grouptransferase'. The common names are normally formed as 'acceptor grouptransferase' or 'donor grouptransferase'.

In many cases, the donor is a cofactor coenzyme that carries the group to be transferred. The aminotransferases constitute a special case. Hydrolases: These enzymes catalyse the hydrolysis of various bonds. Some of these enzymes pose problems because they have a very wide specificity, and it is not easy to decide if two preparations described by different authors are the same, or if they should be listed under different entries.

While the systematic name always includes 'hydrolase', the common name is, in most cases, formed by the name of the substrate with the suffix -ase. It is understood that the name of the substrate with this suffix, and no other indicator, means a hydrolytic enzyme. It should be noted that peptidases have recommended names rather than common names. They differ from other enzymes in that two or more substrates are involved in one reaction direction, but there is one compound fewer in the other direction.

When acting on the single substrate, a molecule is eliminated and this generates either a new double bond or a new ring. The systematic name is formed according to 'substrate group-lyase'. In common names, expressions like decarboxylase, aldolase, etc. In cases where the reverse reaction is the more important, or the only one to be demonstrated, 'synthase' may be used in the name. Ligases: Ligases are enzymes that catalyse the joining of two molecules with concomitant hydrolysis of the diphosphate bond in ATP or a similar triphosphate.

Activating Transcription Factor. Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to loss of function, known as denaturation. Different arrangements of the same 20 types of amino acids comprise all proteins. Two rare new amino acids were discovered recently selenocysteine and pyrrolysine , and additional new discoveries may be added to the list. Proteins are a class of macromolecules that perform a diverse range of functions for the cell.

They help in metabolism by providing structural support and by acting as enzymes, carriers, or hormones. The building blocks of proteins monomers are amino acids. Each amino acid has a central carbon that is linked to an amino group, a carboxyl group, a hydrogen atom, and an R group or side chain. There are 20 commonly occurring amino acids, each of which differs in the R group.

Each amino acid is linked to its neighbors by a peptide bond. A long chain of amino acids is known as a polypeptide. Proteins are organized at four levels: primary, secondary, tertiary, and optional quaternary. The primary structure is the unique sequence of amino acids.