Protamines

are not fullvalue proteins, very small proteins with Mm 6000 D. They contain of 80% diaminomonocarboxylic acid, have very large positive charge and IEP more than 10. They are soluble in salts, acids but are precipitated in alkalis. They are contained in nucleus of fish, reptiles, plants and they regulate of the function of DNA.

Scleroproteinsare unfulvalue proteins, they don not contain all essential a/acids. Second name is proteinoids because their properties sharply differ from all proteins. They are not dissolved in water, weak solutions of neutral salts, are not precipitated (curtailed) by heating, the majority of them is not splitted by enzymes of gastrointestinal tract. They contain of a lot disulfide bonds (bridges).

The p. of connective tissues are proteinoids. In organism of the man and animals there are three kinds of scleroproteins (sp): collagens, elastins, keratins, which differ from each other by structure of molecules and their aminoacid composition. All of them concern to fibrous p. and are constructed from braided as twist α helix or from β-pleated sheet cross-linked by disulfide bonds.

Collagen [C] makes 25-35% of p-s of a body, the unfulvalue protein, formed in fibroblastes, molecular weight 28500 D. It does not dissolve in water. Its molecules have the original aminoacids composition. Everyone third aminoacid is subunitted glycine, 11% - are on share alanine, 21% - proline and oxyproline.

Molecule of collagen have some quantity of the disaccharides but quantity of carbohydrates small and consequently they concern to simple proteins.

The molecule of collagen has the form of a core of length 3000 Å and diameter 15. It is one of the longest proteins. The primary structure of collagen refers to tropocollagen and represents polipeptide chain from 1100 aminoacids.

Secondary structure is a stretched α helix because in the molecule of collagen there are a lot of proline and oxyproline, which prevent the formation and which do their spiral steady for the different action.

Tertiary structure of collagens is a superspiral three polipeptide chains connected by hydrogen bonds.

Quaternary structure is submitted by several three fold spirals, which are stacked up as parallel bunches for a type “a head to tail”. The heads are moved from each other ¼ length that causes striations of their molecules. Quaternary structure is stabilized due to inside molecular and intermolecular covalent bonds between two residues lysine of the parallel chains. Quantity and type of cross bonds depend on the function and age of collagen. High degree of elasticity is caused by quantity of cross linkage. The collagen fibrils have surprising durability: for break of a fibrils by a diameter of 1 mm it is necessary to apply (put) force in 10 kgs.

4 types of C are known. Collagen of the first type is contained in organism in the greatest quantity, meets in skin, tendons, bones, cornea of an eye. The second type of collagen meets in cartilages, glassoid body of an eye. Collagen of the third type is met in intima of vessels and cardiavascullar system, fourth type – in basal membranes. Collagen is the basic component of scar after wound.

At the boiling with acid water collagen is converted to gelatin – easily digested peptide of low nutrition value. Collagen breaks up under action of collagenase with formation hydroxyproline, which level in blood reflects speed of metabolism of collagen.

Elastins are unfulvalue proteins in tendons, sinews, walls of large vessels. They are capable to stretch in some times in length and at removal of loading quickly to restore the initial form. Basic subunit of elastin is tropoelastin with molecular weight 72000 D. There are a lot of alanine and glycine in elastine, especially a lot of lysine.

The spiral of polypeptide chains of tropoelastin differs both from α-helix and from a spiral of collagen. There are sites In tropoelastin in which the residues lysine, participating in formation of cross linkages prevall. Besides in elastine are found out desmosin and isodesmosin in which formation four molecules of lysine participate.

This formation enable of elastin is convertible to stretched in all directions.

Keratins have received the name from greek words and are two kinds of keratins – α and β. Alfa-keratins are proteins of a hair, wool, feathers, horns, nails, needles, scale, hoofs, shell and also significant part of an outside layer of skin. In the structure of α-keratin there is much cysteine. α-keratin consist of three polypeptide chain with spiral characteristic for each one. Besides the bonds between polypeptide chains there are many disulfide “bridges” between cysteins of various chains. Therefore keratins have the large durability. Strongest and rigid α-keratins (in the shell of a turtle) contain up to 18% cystine. They are not dissolved in water.

Β-keratins are proteins of fibroin (fibers of silk and spider’s webbs). Though they are more flexible but hardly give in to a stretching. They have β-pleated sheet. In β-keratin there is a lot of glycine and alanine, for example in fibroin of silk everyone second aminoacids is glycine.

Table 1 “The properties of globular simple proteins”

Property	Albumins	Globulins	Protamins	Histones
Solubility	Water, acids, alkalies and salts	Acids, alkalis and salts	Water and acids
Coagulation	Coagulate in the heating	Don’t coagulate	Coagulate in the presence of salts and alkalis
Mol. weight	70 000 Da	150 000 Da	6 000 Da	12 000 Da
Aminoacid composition	Monoaminodicarboxylic aminoacids: Asp and Glu	Monoaminomo nocarboxylic aminoacids	Diaminomonocarboxylic aminoacids: Lys and Arg 80% 30%
The charge	Large negative	Small negative	Large positive	Small positive
The movement in electric field	To positive charge Quickly slowly	The electrophoresis isn’t applied
Salting-out	By saturated solution of ammonium sulfate	By unsaturated solution of ammonium sulfate	This method isn’t applied
Full value	Full value proteins	unfull value proteins
Spreading in the nature	Animals and plants	Only in the animals Primitive mammals, organisms human, birds
Functions	1) transport of FFA, bilirubin, drugs, hormones, toxins; 2) maintenance of Ponc	1) α-globulins transport lipids and copper and are antiproteinases (proteins of acute phase); 2) β-globulins transport cholesterol and iron; 3) γ-globulins are immunoglobulins	They enter in composition of nucleoproteins and participate in gene expression and stabilization of nucleic acids

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Histones (H)	\|

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