Plasma glycoprotein catabolism

CETP is a hydrophobic plasma glycoprotein, mainly synthesized in the liver, that possesses the unique ability to facilitate the transfer of cholesteryl ester (CE). CETP circulates in the blood, bound predominantly to HDL. CETP mediates the transfer of cholesteryl esters from HDL to VLDL and LDL in exchange for triglycerides. CETP also promotes the transformation of HDL2 to HDL3, an action that could promote reverse cholesterol transport. CETP inhibition produces an increase in HDL by markedly delaying the catabolism of apoA-I and A-II (129), an action that increases reverse cholesterol transport. These actions of CETP suggest that CETP inhibition could prevent atherosclerosis (130-132). 

Ashwell, G., and Morell, A. G., 1971, Galactose A cryptic determinant of glycoprotein catabolism, in Glycoproteins of Blood Cells and Plasma (G. A. Jamieson and T. J. Greenwalt, eds.), pp. 173-189, Lippincott, Philadelphia. 

Most of the plasma proteins are glycoproteins and, except for the ) globulins that are synthesized in lymphoid tissue and the widely distributed cells of the reticuloendothelial system, they are synthesized in the liver. They exist in equilibrium with the tissue proteins and are subject to continuous catabolism and replacement. Nevertheless, homologous plasma proteins (i.e. plasma proteins derived from the same species) appear able to pass into the tissue cells without prior degradation. No particular organ has been shown to be the sole site of catabolism of any one plasma protein. 

Preliminary data are available on the mechanisms whereby glycoproteins are eliminated from the plasma (Winzler, 1968 Bocci, 1970). One possible route of catabolism is leakage into the intestinal tract and subsequent digestion (Schultze and Heremans, 1966b Bocci and Winzler,... 

Making some allowance for the different identities of the plasma proteins listed in Table VI and those mentioned above, there are considerable discrepancies in the circulation time of those labeled in the protein and in the amino sugar residues. The possibility that carbohydrate residues might be removed from glycoproteins before general catabolism of the protein part... 

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