Purpose: To identify water-soluble ascorbate free radical (AFR) reductase in lenses. Materials and Methods: AFR reductase was purified from the water-soluble fractions of rabbit lenses by gel filtration, cation exchange chromatography, isoelectric focusing, and two-dimensional (2-D) gel electrophoresis. Protein spots in 2-D gel were identified using MALDI TOF-MS, and peptide fragment sequences were determined by MALDI TOF/TOF. An expression vector was constructed to produce recombinant AFR reductase. The AFR reductase activity of the recombinant protein was assayed. Results: The active AFR reductase fraction separated from the water-soluble extract of rabbit lenses showed an isoelectric point of pI 8.4, and a molecular weight of approximately 30 kDa. Water-soluble AFR reductase was identified as cytochrome b5 reductase 2 isoform X1 or X2 by MALDI TOF-MS and MALDI TOF/TOF. Recombinant cytochrome b5 reductase 2 showed AFR reductase activity. Conclusions: This study identified water-soluble AFR reductase in lenses as cytochrome b5 reductase 2.
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