Induction, purification and molecular characterization of sulfhydryl oxidase from an Egyptian isolates of Aspergillus niger

The conditions for the sulfhydryl oxidase (SOX) production and activity from an Egyptian isolate of Aspergillus niger were optimized. Purification and determination of the kinetic properties (K _m and V _max) of the purified enzyme have been done. The possibility for the SOX induction using L-Cys (as a natural substrate) was studied to determine whether SOX could be produced as an inducible enzyme in addition to being a constitutive one (i.e. whether induction leads to increase SOX production and activity or not). The optimum temperature and pH for its activity were found to be 60°C and 5.5, respectively. The activity of the induced intracellular SOX, was measured according to Ellman’s method using the standard GSH oxidation where it reached 94% while that of non-induced one reached only 27.6%. This wide difference in activity between the induced and non-induced SOX indicates the successful L—Cys-induction of the SOX production (i.e. SOX from A. niger AUMC 4947 is an inducible enzyme). Molecular characterization of the pure SOX revealed that it is constituted of two 50–55 KDa subunits. K _m and V _max were found to be 6.0 mM and 100 μM/min/mg respectively.