γ‐Polyglutamic Acid Produced by Bacillus Subtilis (Natto): Structural Characteristics, Chemical Properties and Biological Functionalities

Abstract

Abstractγ‐(D,L)‐Polyglutamic acid [γ‐(D,L)‐PGA, or γ‐PGA] produced by Bacillus subtilis (natto) both on laboratory and pilot scale fermenter systems has been characterized. γ‐PGA in its free acid form (H+) is insoluble in water. The salt forms of K+, Na+, NH4+, Ca2+, and Mg2+ of γ‐polyglutamates are fully soluble in water. The structural characteristics of the salts of γ‐Polyglutamates (Na+, K+, NH4+, Ca2+, and Mg2+) were determined with 1H‐ and 13C‐NMR spectroscopy and FT‐IR spectroscopy. The thermal properties were determined with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The typical physical and chemical properties including pH‐titration curve, concentration‐dependent viscosity temperature‐dependent viscosity, and heavy metal binding properties with Pb2+, Cd2+, and Cu2+ were also determined. The biological functionalities were partially characterized with in vivo feeding studies with broilers and egg‐layers, and activation of GTF (Glucose tolerance factor) activity with rat 3T3‐L1 cell culture studies. γ‐(D,L)‐Polyglutamic acid [γ‐(D,L)‐PGA] appears to have five different conformations depending on the environmental conditions. They are the α‐helix, β‐sheet, helix‐to‐random coil transition, random‐coil and enveloped aggregate. The conformational states, hydrogen bonding and polyanionic nature make γ‐PGA a versatile multi‐functional biopolymer possessing many useful biological functionalities.