L-Galactono-γ-lactone dehydrogenase, which catalyzes the final step of the biosynthesis of L-ascorbate, is bound to spinach mitochondrial membrane, as confirmed by linear sucrose density gradient centrifugation. The solubilized enzyme was very labile, but stabilized in the presence of L-galactono-γ-lactone under anaerobic conditions. The enzyme reduced cytochrome c and phenazine methosulfate in the presence of L-galactono-γ-lactone, but not when L-gulono-γ-lactone was used as an electron donor. The Kms of the enzyme for L-galactono-γ-lactone and cytochrome c were 192 μM and 180 μM, respectively.
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Mutsuda et al. (1995) studied this question.