Purification and Partial Characterization of a Genetically-Defined Superoxide Dismutase (SOD-1) Associated with Maize Chloroplasts

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Abstract
The chloroplast-associated form of superoxide dismutase (SOD-1) from maize (Z. mays L.) was purified by a stepwise procedure consisting of (NH4)2SO4 fractionation, G-100 Sephadex gel filtration, DEAE-Sephacel chromatography and hydroxylapatite chromatography. This procedure resulted in a single band on sodium dodecyl sulfate[SDS]-polyacrylamide gels indicating that the preparation is homogeneous. The holoenzyme MW was estimated at 31,000-33,000 by gel filtration. The subunit MW of this dimeric protein was estimated at 14,500 on SDS-polyacrylamide gels. Studies involving amino acid composition analysis, immunological cross-reactivity, in vitro subunit hydbridizations, and H2O2 sensitivity indicate that SOD-1 differs significantly from SOD-2 and SOD-4, the other Cu-Zn forms of SOD from maize. The possible physiological role of SOD-1 within the chloroplast is discussed.

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