The affinity immobilization of a recombinant Schistosoma japonicum glutathioneS-transferase C-terminally fused with a 6 x His peptide, named SjGST/His, was first investigated using Ni2+-chelated metal affinity matrices. The immobilized enzyme retained best activity over a 5-50 mug/mL range of binding protein concentrations, with a high activity yield. Immobilized SjGST/His remained active during 84 days of storage at 4 degreesC, but its activity started to decline considerably after 34-50 days of storage at 25 degreesC, presumably due to extensive proteolytic degradation of the fixed enzymes beginning at their N-termini. Following heat treatment of both free and immobilized forms of wild-type and Cys85 --> Ser, Cys138 --> Ser, and Cys178 --> Ser site-directed mutant SjGST/His, all the immobilized forms retained better activity than their free ones did. In addition, the solid-state refolding study revealed that immobilizing denatured SjGST/His onto Ni2+-chelated gels at a low binding concentration, followed by stepwise washing of the resulting gels with gradual reduction of the denaturant, yielded active and intact enzymes at the final native elution. Under the same optimal conditions, active SjGST/His was successfully recovered from solubilized inclusion bodies. This study demonstrates that it is possible to directly and efficiently immobilize and solid-state refold polyHis-tagged proteins using metal affinity matrices.