Table 2 Composition of the free (transport) lipoproteins in plasma of human

Fractions	Source	nM	Densi ty	Composition
				Pro teins	Total lipid	Percentages of total lipids (100%)
				(%)	(%)	TAG	PHL	CHE	CHF	FFA
CHM	Intes tine	< 1000	< 0.96	2	98	85	8	5	2	-
VLDL	Liver	< 90	< 0.01	10	90	55	20	15	10	-
LDL	CHM Liver	< 30	< 1.06	20	80	15	25	50	10	-
HDL	Liver, intes Tine, CHM, VLDL	< 20	< 1.20	50	50	10	50	25	10	5
Albu min+ FFA	Adipo se tissue	< 5	> 1.30	99	1	-	-	-	-	1

Inside the molecule lipoproteins have the nucleus with lipids such as triglycerides and free cholesrerol. Surrounding this inner core of neutral lipids are located esters of cholesterol, phospholipids and proteins.

In structural lipoproteins which for example composed the cell membranes hydrophilic part is inside of membranes and hydrophobic - outside.

Glycoproteins – specimens, structures, properties, roles

GP (glycos – sweet) have restrictively been defined as conjugated proteins that contain, as a prosthetic group, one or more saccharides lacking a serial repeat unit and bound covalently to a peptide chain (D-galactose, D-mannose, D-glucose, L-fucose, N-acetylglycosamine, N-acetylgalactose, sialic acid, arabinose, neuraminic acid, xylose). Connection between protein and prosthetic group is covalent, carbohydrates-peptides one. Carbohydrates covalently linked to glycoproteins by glycosyl bonds. Covalent linkage of sugars to the peptide chain is a central part of glycoprotein structure, and only a limited number of bond types are found. The carbohydrate attached at one or at multiple points along a polypeptide chain usually contains less than 12-15 sugar residues. In some cases the carbohy­drate component consists of a single sugar moiety, as in the sub maxillary gland gly­coprotein (single N-acetyl-a-D-galactosaminyl residue) and in some types of mam­malian collagens (single a-D-galactosyl residue). In general, glycoproteins contain sugar residues in the D form, except for L-fucose, L- arabinose, and L-iduronic acid; A glycoprotein from different animal species often has an identical primary structure in the protein component, but a variable carbohydrate component. This heterogeneity of a given protein may even be true within a single organism. For example, pancreatic ribonuclease A and В forms have identical amino acid sequences and a similar kinetic specificity toward substrates but differ significantly in their carbohydrate compositions.

Properties of GP

GP have a grate molecular mass, high viscosity, have acid properties, precipitated in acid medium, thermostable, stable to ferments because carbohydrate part. The functions of glycoproteins in the human are of great interest. Glycopro­teins in cell membranes may have an important role in the group behavior of cells and other important biological functions of the membrane. Glycoproteins form a major part of the mucous that is secreted by epithelial cells, where they perform an important role in lubrication and in the protection of tissues lining the respiratory and gastrointestinal systems. Many other proteins secreted from cells into extracel­lular fluids are glycoproteins. These proteins include hormones found in blood, such as-follicle-stimulating hormone, luteinizing hormone, and chorionic gonadotropin; and plasma proteins such as the orosomucoids, ceruloplasmin, plasminogen, prothrombin, and immunoglobulins.

The amount of carbohydrates in glycoproteins is highly variable. Some glycoproteins such as IgG contain low amounts (4%) of carbohydrate by weight, while glycophorin, the human red cell membrane glycoprotein, contains 60% carbohydrate. Human ovarian cyst glycoprotein contains 70% carbohydrate, and human gastric glycoprotein is 82% carbohydrate. The carbohydrate can be distributed along the polypeptide chain or concentrated in defined regions. For example, in hu­man glycophorin A the carbohydrate is found in the NH₂-terminal half of the polypeptide chain that lies on the outside of the cellular membrane.

GP