Publisher Summary Poly (γ-glutamic acid) (PGA) is a bacterial polypeptide in which glutamic acid residues are extensively polymerized via linkage between the γ -carboxyl and amino groups. PGA has been attracting industrial attention because of its extremely viscous property as well as high water-retaining ability. It is generally accepted that PGA exists as a mixture of optically homogeneous peptides such as poly (γ -D-glutamic acid) (D-PGA) and poly (γ -L-glutamic acid) (L-PGA. D-PGA was predominantly isolated as the capsular component of Bacillus anthracis and B. polymyxa, whereas L-PGA was isolated from the cell wall component of an alkalophilic strain of B. subtilis. L-PGA is also found in nematocysts from Hydra as an example of PGA distribution in eucaryotic cells. In these PGA preparations, however, either the L- or D-glutamic acid residue is detected as a minor component in addition to the other optical isomer as the major constituent of the molecule. The production of these oligopeptides makes the whole structure of PGA more complex than expected from the structure of F-I itself. Such an optically heterogenous structure should give it a high viscosity and some other relating properties of industrial interest.