Enzyme activities in the gel were detected by the precipitation of formazan from iodonitrotetrazolium (INT). NADP-ICDH activity was tested by incubating BN gels with isocitrate (5mM), NADP+ (0.5mM), 0.4 mg/mL INT and 0.2 mg/mL phenazine methosulphate (PMS) in activity buffer.