Microstructure of poly(gamma-glutamic acid) produced by Bacillus subtilis consisting of clusters of D- and L-glutamic acid repeating units

Poly(gamma-glutamic acid) (PGA) produced by a strain of Bacillus subtilis was partially hydrolyzed into various oligopeptides so that the dipeptide fraction was isolated by the preparative thin-layer chromatography. HPLC analysis was applied to the detection of each of the four stereoisomers in this fraction using chemically synthesized authentic samples. The fraction consisted of N-gamma- d-glutamyl- d-glutamic acid, N-gamma- l-glutamyl- l-glutamic acid, N-gamma- d-glutamyl- l-glutamic acid, and N-gamma- l-glutamyl- d-glutamic acid at a ratio of 5.9:6.0:1.0:1.0. On the basis of this result, a model was proposed for the microstructure of the bacterial PGA, in which d- and l-glutamic acid repeating units are alternately linked in a single chain of the molecule.