Production of L-leucine aminopeptidase by selected Streptomyces isolates

AIMS: To screen various Streptomyces cultures producing L-leucine aminopeptidase (LAP). METHODS AND RESULTS: Twenty-one Streptomyces strains were screened for LAP production. The best three producers were found to be Streptomyces mobaraensis NRRL B-3729, Streptomyces gedanensis IFO 13427, and Streptomyces platensis NRRL 2364. pH optima of the three enzymes were in the range of 8.0-8.5 and the temperature optima varied between 50 and 65 degrees C. LAP of S. mobaraensis was stable at 60 degrees C and pH 8.5 for 60 min. Metal ion salts, CoCl(2).6H(2)O and ZnSO(4).7H(2)O in 0.7 mmol l(-1) concentration enhanced the relative enzyme activity in all three enzymes. Molecular mass of LAP of S. mobaraensis was found to be approx. 37 kDa. CONCLUSIONS: Streptomyces mobaraensis NRRL B-3729, S. gedanensis IFO 13427, and S. platensis NRRL 2364 were found to be good producers of extracellular LAP. The approx. 37 kDa enzyme of S. mobaraensis is considerably thermostable. SIGNIFICANCE AND IMPACT OF THE STUDY: A good number of Streptomyces were screened and the ability of the aminopeptidases to release a particular N-terminal amino acid along with its good thermal stability makes them interesting for controlling the degree of hydrolysis and flavour development for a wide range of substrate.