Microstructure of poly(γ-glutamic acid) produced by Bacillus subtilis consisting of clusters of D- and L-glutamic acid repeating units
Poly(γ-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-γ-D-glutamyl-D-glutamic acid, N-γ-L-glutamyl-L-glutamic acid, N-γ-D-glutamyl-L-glutamic acid, and N-γ-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.
Synthesis of γ-Glutamyl Peptides Catalyzed by Transamidase from Bacillus natto
Crude ammonium sulfate fraction of a cell free extract from Bacillus natto contained an enzyme (or enzymes) which catalyzed the transamidation reaction specific for glutamine.Both L- and D-isomers of glutamine were active as substrate.On incubation of L- or D-glutamine with the enzyme preparation, two peptides consisting of glutamic acid and glutamine were formed.The main component of the peptides was readily isolated by ion-exchange chromatography and identified as γ-glutamylglutamine by paper chromatography and by paper electrophoresis using authentic peptides.The optical configuration of the amino acid residues in the dipeptide was determined by digestion of the acid hydrolyzate with L-glutamic acid decarboxylase, and the result showed that the dipeptide obtained from L-glutamine was a L-L isomer, while the dipeptide from D-glutamine was a D-D isomer.