Abstract
Apoascorbate oxidase has been shown to have a molecular weight of 137,000 ± 3,000 and essentially the same gross quaternary conformation as native ascorbate oxidase. The apoenzyme, however, lacks much of the conformational stability of the native enzyme. The removal of the copper from the oxidase protein, and the simultaneous reduction of the disulfide bonds results in an apoenzyme of lower structural stability than the native oxidase. The aging of apoascorbate oxidase has been found to involve a loss of ionizable tyrosine residues and a dissociation to subunits and component polypeptide chains, which was not observed with the more stable native and holoenzymes. The molecular weight of holoascorbate oxidase has been determined to be 285,000. An s 20,ω 0 of 9.79 has been determined for the holoenzyme. Holoascorbate oxidase has been shown to have an electrophoretic mobility on polyacrylamide gels that is 23% lower than either the native or apoenzyme. Furthermore, electrophoresis of the holoenzyme in buffers containing dodecyl sulfate, and also isoelectric focusing of the holoenzyme, produce patterns of greater similarity to those of apoascorbate oxidase than the native enzyme.
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