Proteins

The amount of protein can be measured in the number of amino acids or in the Dalton (molecular weight), often because of the relatively large size of the molecules in the derivatives units - kilodaltonah (kDa). Proteins of yeast, on average, composed of 466 amino acids and have molecular mass of 53 kDa. The largest of the currently known proteins - Titina (other names: taytin, konnektin) - is a component sarkomerov muscles; molecular weight of the different isoforms varies in the range of 3 000 to 3 700 kDa, with a total length of 38 138 amino acids (in human muscle solius).

Proteins are also amphoteric polyelectrolytes (poliamfolitami), the groups capable of ionization in solution, are residues of carboxylic acid side chains of amino acids (aspartic and glutamic acid) and nitrogen side chains of basic amino acids (particularly ?-amino group of lysine and amidinovy balance CNH (NH2) of arginine, to a lesser extent - imidazolny histidine residue). Proteins as poliamfolity characterized by isoelectric point (pI) - acidity pH environment in which a molecule of the protein does not carry electric charge and, accordingly, do not move in an electric field (eg, in electrophoresis). The value of pI is determined by the ratio of acidic and basic amino acid residues in proteins: an increase in the number of basic amino acid residues in the protein leads to an increase in pI; increase in the number of acidic amino acid residues leads to a reduction in value of pI.

The significance of isoelectric point is a characteristic constant of proteins. Proteins with pI lower than 7 are called acidic, and the proteins with pI more than 7 are considered major. In general, pI protein depends on the functions performed by them: Isoelectric point of proteins of most tissues of vertebrates lies in the range of 5.5 to 7.0, but some cases are at the extreme values of both fields, for example, pepsin - an enzyme proteoleticheskogo silnokislogo gastric pI ~ 1, and for salmina - milk protein-protamine of salmon, which is to feature extremely high content of arginine, pI ~ 12. Proteins associated with nucleic acids through electrostatic interactions with the phosphate residues of nucleic acids are often the main protein. Examples of such proteins serve as histone and protamine.

Depending on the degree of solubility in water, proteins are soluble (hydrophilic) and insoluble (hydrophobic). The latter include most members of the biological membrane of integral membrane proteins that interact with the hydrophobic membrane lipids.