Examination of the Potential Role of 7-Carboxyglutamic Acid in Eggshell Quality1

ABSTRACT The outer portion of the outer shell membrane of hen eggs was removed, subjected to alkaline hydrolysis and analyzed for 7-carboxyglutamic acid (Gla) via amino acid analysis. Although the presence of a ninhydrin positive substance was found in close proximity to the Gla reference peak, gas chromatographic-mass spectrophotometric analyses of this peak revealed that it was not Gla. 7-Carboxyglutamic acid has been recently found in the shell matrix, and it was of interest to determine if the presence of Gla in the shell matrix is essential for the production of a strong shell. This was accomplished by feeding hens a vitamin K antagonist and evaluating their eggs for shell quality. Although prothrombin times were significantly increased, no significant changes occurred in the specific gravity measurements of eggs laid during the 14 days of treatment. This information strongly suggests that the carboxylation of glutamic acid is not an essential step in the formation of a strong eggshell