PURIFICATION AND CHARACTERIZATION OF A NEWLY SCREENED MICROBIAL PEPTIDE AMIDASE

A microbial peptide amidase was found in a limited screening and purif ied about 500-fold from Stenotrophomonas maltophilia. The native enzym e has a molecular mass of 38 kDa (gel filtration). The sequence of the first 16 amino acids was determined by Edman degradation. The isoelec tric point was found to be around 5.8. The peptide amidase exhibited a pH optimum of 6.0 and a temperature optimum of about 39-45 degrees C. The enzyme is stable in 50 mM TRIS/HCl, pH 7.5, at 30 degrees C, and the residual activity was found to be above 90% after 1 week of incuba tion. The biocatalyst is not inhibited by potential inhibitors like Hg 2+, EDTA, D-cycloserine or dithiothreitol and only weakly influenced b y inhibitors of serine proteases. The peptide amidase deamidates selec tively C-terminal amide groups in peptide amides without hydrolysing i nternal peptide bonds or amide functions in the side-chain of glutamin e or asparagine. Unprotected amino acid amides are not hydrolysed. The enzyme is stereoselective with regard to L-enantiomers in the C-termi nal position.