Purification and biochemical characterization of l-glutaminase from Aspergillus oryzae with potential biotechnological applications in synthesis of l-theanine and as antitumor agent

Fungal glutaminase is of great importance in different industries fields. Thus, searching for a significantly catalytic L-glutaminase (Glut) with appraising its biochemical properties and biotechnological applications are the main purposes of this work. The Glut from Aspergillus oryzae was purified with a specific activity 258.33 (U/mg of protein), 215-fold and 36.47% yield. The molecular weight of the purified enzyme was 65 kDa. The purified enzyme exhibited remarkably improved resistance toward higher temperature in the presence of an exogenous trehalose. The enzyme had a greater affinity towards L-glutamine, L-cysteine, L-proline and L-lysine than L-valine, and L-glycine. The essentiality of arginine, tryptophan, histidine, and cysteine residues in the catalysis process of L-glutaminase was determined. The application of biocatalyst in the reaction mixture has not only remarkably increased L-theanine concentration but also has enhanced glutamic acid production in the presence of 10% compared with 15% NaCl. The deamidation of water insoluble Zea or rice glutelin was approximately 65% and 83% after 44 h by the enzymatic treatment. The purified Glut displayed remarkable antitumor activities against lung (A549), liver (HepG2) and human breast (MCF-7) carcinoma. Thus, L-Glut from A. oryzae has the potential to be used in food application and in treatment of various cancer cells.