Protein

Protein is an organic compound of high molecular weight ranging from several thousand to millions. This protein is composed of atoms C, H, O and N and the other two elements such as P and S which form the amino acid units. These amino acids can be divided according to their chemical structure (aliphatic, aromatic, heterocyclic) or according to its R group.

Proteins are macromolecular polypeptides composed of a number of L-amino acids linked by peptide bonds. A protein molecule composed by a number of specific amino acids with a particular arrangement that has been and is also derived. At pH 7 or greater, is always negatively charged roteins, positive and non metallic charge neutralize the protein content and soluble protein is not anymore.
The properties of the amino acids that is almost all amino acids are not soluble in water and soluble in non polar solvent / organic such as ether, chloroform and acetone unless both carboxylic acid and aliphatic or aromatic organic amines. Amino acid crystals have a rather high melting point.
Determination of quantity and type of amino acid
Peptide bond linking the first amino acid with hidrolisisis disconnected. Free amino acids that have been then identified by chromatography or elektroforesisi. The number of amino acids was then calculated after mereaksikannya with tau ninhydrin color reaction that is typical or the spectrum of amino acids and other aromatic-lan. Peptide bond can puladihidrolisisi with acids, bases or enzymes.
Some reactions Proteins
1. With concentrated mineral acids precipitate the protein but = would be late returning the deposit if excessive acid.
2. Basa did not cause precipitation of the protein but resulted in hydrolysis and oxidative decomposition.
3. Heavy metals precipitate the proteins, depending on temperature and other elketrolit. Mercury chloride and silver nitrate to form deposits that can not be dissolved again while sulfate and feriklorida produces sediment which can be dissolved again.
4. Alkoloidal reagent such as trichloroacetic acid, acid tannat, fosfotungstat acid, ascorbic acid functions as a settling fosfomobolibdat protein when pH is more acidic than the protein isolistrik point.
5. Alcohol or an organic solvent are also settling in protein and more effectively at the point isolistrik proteins.
6. The heat causes coagulation of proteins with an effective temperature ranges between 38-750C. several factors affect these coagulation proteins but most easily at the point isolistriknya berkoagulasi. Insoluble coagulum except if the solvent can hydrolyze or break it.
Some Color Reactions of Protein
1. Millon reaction
This reaction is used to memerikasa triftofan in the protein molecule. Add 3 to 4 drops of Millon reagent into 5 ml of protein solution. Mix together and reheat. White precipitate that immediately arises slowly turn red. This reaction can not take place if the protein is not precipitated by concentrated acid.
2. Biuret Reaction
Add 2-3 drops of alkaline and Cu-sulfate solution (approximately 0.02 percent). Color change occurs, depending on the type of protein. This experiment is typical for peptide bond.
3. Reaction Xantoprotein
Nitric acid were added to the protein solution causes the yellow color turned into orange if added bases. This reaction occurs when the protein was found in the amino acid with an aromatic nucleus such as triftopfan, tyrosine, phenylalanine nd.
4. Experiment Hopkins-Cole
This reaction is specific for the amino acid tryptophan. Tryptophan-containing material to form violet color at the boundary between the material and glyoxylate acid.
5. Ninhydrin reaction
This reaction is useful for all protein-containing compounds of at least one carboxyl group and an amino group which is free.
Protein denaturation
Most biologically active proteins functioned only on regional pH and temperature are limited. If the pH and temperature changes across these boundaries, will experience a denaturation of proteins. Because the enzyme is a protein, then the case of denaturation, the enzyme will lose its biological activity. In this case the peptide bond does not change that changes is the form of pleats. The process of returning to original form after denaturation called renaturation. For this pengembalin unnecessary chemicals, usually occur because of changes in pH or temperature.