γ Carboxyglutamic acid. Identification and distribution in vitamin K dependent proteins

G. L. Nelsestuen, T. H. Zytkovicz, J. B. Howard

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Abstract

γ Carboxyglutamic acid, (HOOC)2CH CH2 CH(NH2) COOH, was demonstrated to be a component of prothrombin and was found in a peptide that was shown by other methods to contain at least a portion of the vitamin K dependent sites in prothrombin. The vitamin apparently is required for the incorporation of the second carboxyl group onto the glutamic acid side chain. The vitamin K dependent sites on prothrombin are responsible for the property of calcium binding, which is essential for the physiologic conversion of prothrombin to thrombin, and for the property of quantitative adsorption of prothrombin onto precipitates of barium salts. The γ carboxyglutamic acid evidently is responsible for these characteristics. There are at least 10 γ carboxyglutamic acid residues in prothrombin, all of which are located in the nonthrombin region of the protein. Bovine Factor X contains at least 14 residues of γ carboxyglutamic acid located in the light chain. Reduction of the carboxyl groups of intact vitamin K dependent proteins with [3H]diborane followed by hydrolysis releases 5,5' dihydroxyleucine, the reduction product of γ carboxyglutamic acid, which can be identified by amino acid analysis. Because direct analysis of γ carboxyglutamic acid is complicated by its decarboxylation during acid hydrolysis to yield glutamic acid, this procedure is valuable in identifying other metal ion chelating proteins that contain γ carboxyglutamic acid.

Original languageEnglish (US)
Pages (from-to)941-944
Number of pages4
JournalMayo Clinic Proceedings
Volume49
Issue number12
StatePublished - Dec 1 1974

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