Glycolate oxidase (GO) isozyme with high specific activity (75.0～279.0 U/mg) is purified quickly on DEAE- Cellulose column from Brassica parachinensis Bailey. Its pI is greater than 10.0 assayed by acetate cellulose membrane electrophoresis for 1 hour. In view of about ten kinds of pI varied from 4.5 to 10.0 are observed when the same GO isozyme is assayed in IEF for 14 hours, it is obvious that its pI decreases in IEF. Its pI also decreases when this GO isozyme is assayed in PAGE for 14 hours. Based on the results in SDS-PAGE, CGE-SDS, and IEF, it is most likely that this GO isozyme comprises two noncovalently associated 66 kD basic subunit and 40 kD acidic subunit, the phenomenon of pI change is related to subunit dissociation. The basic/acidic amino acid residues ratios in GO isozyme and its 40 kD acidic subunit are detected to be 0.66 and 0.54, respectively, a value much lower than that (0.96) in 40 kD peptide encoded by GO cDNA reported previously, indicating neither M r nor charge characteristic of this 40 kD peptide is similar to that of GO isozyme subunits, two subunits of GO isozyme may be the modified products of the same GO gene after post-translation.
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References
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