Abstract

A soluble Cr(VI) reductase was purified from the cytoplasm of Escherichia coli ATCC 33456. The molecular mass was estimated to be 84 and 42 kDa by gel filtration and SDS-polyacrylamide gel electrophoresis, respectively, indicating a dimeric structure. The pI was 4.66, and optimal enzyme activity was obtained at pH 6.5 and 37^oC. The most stable condition existed at pH 7.0. The purified enzyme used both NADPH and NADH as electron donors for Cr(VI) reduction, while NADPH was the better, conferring 61% higher activity than NADH. The K_m values for NADPH and NADH were determined to be 47.5 and 17.2 umol, and the V_max values 322.2 and 130.7 umol Cr(VI) min^-1mg^-1 protein, respectively. The activity was strongly inhibited by N-ethylmalemide, Ag^2+, Cd^2+, Hg^2+, and Zn^2+. The antibody against the enzyme showed no immunological cross reaction with those of other Cr(VI) reducing strains.

• Keywords: Cr(VI) reductase; Escherichia coli ATCC 33456; purification