Chelation of Calcium Ions by Poly(γ-Glutamic Acid) from Bacillus subtilis (Chungkookjang)

Many studies have clarified that poly(γ-glutamic acid) (PGA) increases the solubility of Ca 2+ , suggesting that PGA enhances calcium absorption in the small intestine. However, there has been no report on the specific interaction between PGA and Ca 2+ in water. We studied the aqueous solution properties of PGA calcium salt (PGA-Ca complex). The chelating ability and binding strength of PGA for Ca 2+ were evaluated. The PGA-Ca complex was soluble in water, in contrast to the insolubility of poly(acrylic acid) (PAA) calcium salt, and the chelating ability of PGA for Ca 2+ was almost the same as that of PAA. The globular conformation of the PGA-Ca complex in water was estimated by SEC and viscosity measurements. The chelation ability of PGA for Ca 2+ was examined by 1 H NMR. The present study showing the characteristics of the PGA-Ca complex will provide useful information about the calcium absorption by PGA in vivo.