Characterization and immobilization of purified Aspergillus flavipes L-methioninase: continuous production of methanethiol

Aims: To immobilize the purified Aspergillus flavipes L-methioninase on solid carriers for continuous production of methanethiol with high purity, by the enzymatic methods. Methods and Results: The purified L-methioninase was immobilized using different methods, and physicochemical and kinetic studies for the potent immobilized enzyme were conducted parallel to the soluble one. The activity of the purified extracellular enzyme was 1 8-fold higher than intracellular one from submerged cultures of A. flavipes. Among the tested methods, polyacrylamide (42.2%), Ca-alginate (40.9%) and chitin (40.8%) displayed the highest immobilization efficiency. The thermal inactivation rate was strongly decreased for chitin-immobilized enzyme (0.222 s(-1)) comparing to soluble enzyme (0.51 s(-1)). Enzyme immobilization efficiency was greatly improved using 4 0% glutaraldehyde and 41.6 /6.3 (T/C) as spacers for chitin and polyacrylamide-enzyme conjugates, comparing to their controls. Also the incorporation of lysine, glutathione, cysteine and dithiothreitol as active site protectants significantly enhance the catalytic efficiency of immobilized enzyme. The activity of enzyme was increased by 4.5- and 3.5-fold using glutathione plus DDT and glutathione plus methionine, for chitin and polyacrylamide enzyme, respectively. Conclusion: Chitin enzyme gave a plausible stability till fourth cycle for production of methanethiol under controlled system. Applying GC and HNMR analysis, methanethiol has identical chemical structure to the standard compound. Significance and Impact of the Study: Technically, a new method for continuous production of pure methanethiol, with broad applications, was developed using a simple low expenses method.