Oligomerization of L-gamma-carboxyglutamic acid

Unlike glutamic acid, L-gamma-carboxyglutamic acid does not oligomerize eff iciently when treated with carbonyldiimidazole in aqueous solution, However , divalent ions such as Mg2+ catalyze the reaction, and lead to the formati on of oligomers in good yield. In the presence of hydroxylapatite, L-gamma- carboxyglutamic acid oligomerizes efficiently in a reaction that proceeds i n the absence of divalent ions but is further catalyzed when they are prese nt. After 'feeding' 50 times with activated amino acid in the presence of t he Mg2+ ion, oligomers longer than the 20-mer could be detected. The effect of hydroxylapatite on peptide elongation is very sensitive to th e nature of the activated amino acid and the acceptor peptide. Glutamic aci d oligomerizes more efficiently than L-gamma-carboxyglutamic acid on hydrox ylapatite and adds more efficiently to decaglutamic acid in solution. One m ight, therefore, expect that glutamic acid would add more efficiently than L-gamma-carboxyglutamic acid to decaglutamic acid on hydroxylapatite. The c ontrary is true - the addition of L-gamma-carboxyglutamic acid is substanti ally more efficient. This suggests that oligomerization on the surface of h ydroxylapatite depends on the detailed match between the structure of the s urface of the mineral and the structure of the oligomer.