Transferrin carbohydrate chains

Alcohol consumption is very difficult to assess. There is widespread belief that individuals underreport their intake and there are no reliable laboratory tests available for definitive diagnosis of alcohol abuse. A combination of abnormalities in the plasma activity of gamma-glutamyl transferase (GGT or yGT), AST and reduction in erythrocyte mean cell volume (MCV) maybe useful and all are routine lab. tests. A potential marker of interest is carbohydrate-deficient transferrin (CDT) which is an abnormal isoform of serum transferrin arising due to defects in the attachment of carbohydrate chains to the protein core. Unfortunately, CDT is a somewhat specialized test, not performed by most laboratories. Other markers which have attracted some research interest are ethyl sulphate and ethyl glucuronide. Excretion in the urine of these metabolites occurs for up to 50 hours after binge drinking so they offer a useful index of recent heavy alcohol intake. 

Jamieson, G. A. Studies on glycoprotein II Isolation of the carbohydrate chains of human transferrin. J. Biol. Chem. 240, 2914 (1965). 

A final point of general organization concerns the carbohydrate. All transferrins so far characterized, except apparently for one fish transferrin (84), are glycoproteins. There is, however, no pattern to the sites of attachment of the carbohydrate chains on different proteins—they appear almost randomly distributed over the protein surface (Fig. 4), strengthening the view that the carbohydrate plays no direct role in function. Rabbit serum transferrin, for example, has one carbohydrate chain, on its C-lobe (residue 490) human serum transferrin has two, both on the C-lobe (residues 416 and 611) human lactoferrin has two, one on each lobe (at residues 137 and 478) and bovine lactoferrin has four, one on the N-lobe (residue 233) and three on the C-lobe (residues 368, 476, and 545). 

Secretion of nonglycosylated macromolecules in the presence of tunicamycin has also been investigated in a number of other cells. Rat-liver cell-secretion ol albumin (a carbohydrate-free protein), transferrin, and a-acid glycoprotein was not inhibited, and, in chick-liver cells, only a decrease by 10-25% in the secretion of transferrin and the apoprotein B chain of very-low-density lipoprotein was noted.463,464 The secretion of ovalbumin (a glycoprotein) from hen oviduct was not blocked by tunicamycin.465... 

Capillary electrophoresis has proven to be useful in characterizing different molecular forms of various metalloproteins like metallothionein, transferrin, and conalbumin [2-5]. Molecular forms arise from differences in the amino acid sequence of proteins (isoforms), differences in the amount or type of metal bound (metalloforms), or from differences in the type and amount of carbohydrate side chains linked to the protein (glycoforms). CZE was used to follow the formation of the oligomeric iron core and its incorpora-... 

In conclusion, the characteristics of the carbohydrate moieties of transferrins are specific to each of them on the basis of the primary structure of glycans and of their number and position in the peptide chain as demonstrated in Figs. 2 to 4. In addition, each transferrin presents unexplained microheterogeneity. 

The transferrins are glycoproteins (i.e. compounds of proteins and carbohydrates) and include serum transferrin, lactoferrin (present in milk) and ovotransferrin (present in egg white). In humans, serum transferrin transports 40 mg of iron per day to the bone marrow. It contains a single polypeptide chain (molecular weight of 80000) coiled in such a way as... 

Transferrin has two bi-antennary carbohydrate side chains that can contain up to six sialic acid... 

Yamashita, K. Ideo, H. Ohkura, T. Fukushima, K. Yuasa, I. Ohno, K. Takeshita, K. Sugar chains of serum transferrin from patients with carbohydrate deficient glycoprotein syndrome. Evidence of asparagine-N-linked oligosaccharide transfer deficiency. J. Biol Chem. 1993, 268, 5783-5789. 

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