Abstract
Since L-prolyl diketopiperazines, L-prolyl-L-valine anhydride and L-leucyl-L-proline anhydride, had been isolated from the culture filtrate of Streptomyces sp. S-580, the mechanism of L-prolyl diketopiperazine formation by Streptomyces has been studied. These two L-prolyl diketopiperazines were not formed from their constituent amino acids incubated with intact cell or cell free homogenate of this strain in buffered salt solution containing energy source. However, from milk casein, poly peptone or gelatin, the former two were components of the culture medium of this strain, hydrolyzed with the pure streptomyces-protease, these L-prolyl diketopiperazines were obtained (only from gelatin, glycyl-L-proline anhydride were obtained in addition to these two). Furthermore, in hydrolysis of some synthetic L-prolyl peptides with this enzyme, L-prolyl diketopiperazine formation were also studied, and as the result, glycyl-L-proline anhydride was obtained from glycyl-L-prolyl-L-leucine but no L-prolyl diketopiperazine was formed from L-prolyl-L-leucyl-glycine. From these evidences, the possible route of L-prolyl diketopiperazine formation by Streptomyces has been discussed.
