Molecular structure and subcellular localization of spinach leaf glycolate oxidase

Glycolate oxidase (E.C. 1.1.3.1) was purified from spinach leaves (Spinacia oleracea). The molecular weight of the native protein was determined by sucrose density gradient centrifugation to be 290,000 daltons (13S), whereas that of the monomeric form was 37,000 daltons. The quaternary structure of the holoenzyme is likely to be octameric, analogous to pumpkin cotyledon glycolate oxidase [Nishimura et al, 1982]. The subcellular localization of the enzyme was studied using linear sucrose density gradient centrifugation, and it was found that glycolate oxidase activity is detectable in both leaf peroxisomal and supernatant fractions, but not in chloroplasts and mitochondria; the activity distribution pattern is essentially similar to that for catalase, a known leaf peroxisomal enzyme. Ouchterlony double diffusion and immunotitration analyses, demonstrated that the rabbit antiserum against purified spinach leaf glycolate oxidase cross-reacted, identically, with the enzyme molecules present in two different subcellular fractions, i.e, the leaf peroxisome and supernatant fractions. It is thus concluded that the enzyme present in the supernatant is due to the disruption of leaf peroxisomes during the isolation, and hence glycolate oxidase is exclusively localized in leaf peroxisomes in spinach leaves.