PGA like the other poly(amino acid)s is a degradable polymer. The polymer can withstand temperatures up to 60 ° C, beyond which the amide bonds start getting hy­drolyzed. PGA is resistant to proteases that cleave alpha peptide bonds. Two types of enzymes are involved in the degradation of PGA, endo-g-glutamyl peptidase and exo-g-glutamyl peptidase. Exo-g-glutamyl pepti­dase consists of two subunits and is a key enzyme in glutathione metabolism (Ogawa et al., 1991; Xu and Strauch, 1996). This enzyme catalyzes the formation of g-glutamic acid di — and tripeptides in vitro. Endo-g — glutamyl peptidase is secreted into the medium by g-PGA-producing B. subtilis and B. licheniformis. It subsequently cleaves high molecular weight g-PGA into fragments as small as 105 Da (Goto and Kunioka, 1992). Attempts to isolate microbes that can utilize PGA as the sole source of carbon and nitrogen source were also successful (Obst and Steinbuchel, 2004).

APPLICATIONS OF PGA

PGA has been a keen interest of research as far as ap­plications are concerned and hence a plethora of appli­cations for this biopolymer has been developed. PGA has been used in the food industry as an additive to flour to increase the moisture-retaining capacity of the dough, as well as to improve the texture and shelf life of bread. The calcium salt of g-PGA can be added to health food in order to increase the Ca2+ concentration, thus contributing to the prevention of osteoporosis (Ashiuchi et al., 2004). Addition of PGA improved the solubility and hence the availability of vitamins and also caused sustained release of these vitamins, which led to increased absorption of these vitamins. PGA salts are known to be used as antifreeze agents in food. The anti­freeze action of the salt increases with the decreasing size of the salt of the polymer (Shih et al., 2003). PGA has been suggested for water treatment, as PGA com­plexes with a lot of metal ions, like Ca+2, Fe+3, Al+3, etc. (Kunioka, 2004). Esters of PGA have been used to test the ability of PGA to form bioplastics with required properties (Kubota et al., 1995). Hydrogels that can be used for applications such as controlled drug release, biosensors, diagnostics, and bioseparators can be pro­duced by using g-PGA and poly(ethylene glycol — methacrylate (Yang et al., 2002). PGA has been used as adjuvants in vaccines, and also as a delivery agent for hydrophobic drugs, increasing their bioavailability. PGA has also been used as a medical adhesive for surgi­cal wounds (sutureless wound closure). PGA hydrogels can be used as three-dimensional scaffolds for tissue en­gineering (Matsusaki et al., 2005).