Glutamyl residues

Work in the mid-1970s demonstrated that the vitamin K-dependent step in prothrombin synthesis was the conversion of glutamyl residues to y-carboxyglutamyl residues. Subsequent studies more cleady defined the role of vitamin K in this conversion and have led to the current theory that the vitamin K-dependent carboxylation reaction is essentially a two-step process which first involves generation of a carbanion at the y-position of the glutamyl (Gla) residue. This event is coupled with the epoxidation of the reduced form of vitamin K and in a subsequent step, the carbanion is carboxylated (77—80). Studies have provided thermochemical confirmation for the mechanism of vitamin K and have shown the oxidation of vitamin KH2 (15) can produce a base of sufficient strength to deprotonate the y-position of the glutamate (81—83). 

Folic acid or folate (Fig. 1) is the collective name for more than 100 derivatives of pteroyl-mono-L-gluta-mate. In plant and animal tissues, folic acid mostly occurs as pteroyloligo-L-glutamate (PteGluJ, with up to eight glutamyl residues. 

A similar set of conditions was utilized by Reif et al.76 to analyze folic acid, using leucovorin as an internal standard. Other authors77 have used similar conditions to study extensively the identity of possible leucovorin contaminants. In addition to these partition /ionization surpression methods, anion exchange hplc has been used to separate CF from other naturally occurring folates,78 and some correlation has been made between the number of glutamyl residues and retention time. 

This is a set of enzymes that act on peptide bonds containing a glutamyl residue. They include ... 

This enzyme [EC 2.3.2.13], also known as protein glutamine y-glutamyltransferase, catalyzes the calcium ion-dependent reaction of the side chain of a glutamyl residue in a protein with an alkylamine to generate an A -alkylglutaminyl residue in the protein and ammonia. 

After the conjugation reaction, the first catabolic step, removal of the glutamyl residue, is catalyzed by the enzyme y-glutamyltranspeptidase (glutamyltransferase). 

In the acidic pH region, it was found that one AO molecule interacts with three glutamyl residues in PLGA using a variation method 152,153). Since AO molecules... 

Drijhout and Bloemhoff142 introduced a thiol-functionalized core based on the K2K unit by coupling A-(5-acetylsulfanylacetyl)glutamyl residues to the amino groups (Scheme 9). Subsequently, Baleux and Dubois[92] prepared a thiolate core based on a similar design by... 

Unaltered folic acid is readily and completely absorbed in the proximal jejunum. Dietary folates, however, consist primarily of polyglutamate forms of N 5-methyltetrahydrofolate. Before absorption, all but one of the glutamyl residues of the polyglutamates must be hydrolyzed by the enzyme -1-glutamyl transferase ("conjugase") within the brush border of the intestinal mucosa. 

It seems that the negative charges can also be on a peptide chain. Fujimaki describes the bitter masking action of peptides rich in glutamyl residues (29 ) and the isolation and identification of acidic oligopeptides from a flavour-intensifying fraction from fish protein hydrolysate (30). 

Compounds with vitamin K activity (Table 6.2) are required in our diets for y-carboxyglutamate biosynthesis (Table 4.1). This amino acid is produced from certain protein glutamyl residues by carboxylation. Proteins that contain y-carboxyglutamate are blood prothrombin and coagulation factors VII, IX, and X (see Chapter 7). Other proteins of this type are osteocalcin from bone and several kidney and muscle calcium-binding proteins. 

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