L-Asparaginase from Aspergillus spp. : production based on kinetics, thermal stability and biochemical characterization

Abstract

This study describes the production of native L-asparaginases by submerged fermentation from Aspergillus strains and provides the biochemical characterization, kinetic and thermodynamic parameters of the three ones that stood out for high L-asparaginase production. For comparison, the commercial fungal L-asparaginase was also studied. Both commercial and L-asparaginase from Aspergillus oryzae CCT 3940 showed optimum activity and stability in the pH range from 5 to 8 and the asparaginase from Aspergillus niger LBA 02 was stable in a more alkaline pH range. About the kinetic parameters, the denaturation constant increased with the heating temperature for all L-asparaginases, indicating that the L-asparaginase activity decreased at higher temperatures, especially above 60 °C. Moreover, L-asparaginase from A. oryzae CCT 3940 remained stable after 60 min at 50 °C. None of the L-asparaginases were inhibited by high NaCl concentrations, which are highly desirable for food industry application. The catalytic activities of all the L-asparaginases were enhanced by the presence of Mn2+ and inhibited by p-chloromercuribenzoate and iodoacetamide. The L-asparaginase from the Aspergillus strains and the commercial enzyme had similar Km when L-asparagine was used as substrate. None of the L-asparaginases, except the L-asparaginase from A. niger LBA 02, could hydrolyze the substrate L-glutamine, which is of interest for medical proposes, since the glutaminase activity is usually related to adverse reaction during the leukemia treatment. This study showed that these new three non-recombinant L-asparaginases studied have potential application in the food and pharmaceutical industries, especially due to their good thermostability