Glutamate:glyoxylate aminotransferase had been reported to be present exclusively in the peroxisomes of plant leaves and to participate in the glycollate pathway in leaf photorespiration (Tolbert (1971) Annu. Rev. Plant Physiol. 22, 45-74]. Glutamate:glyoxylate aminotransferase activity was already present in the etiolated cotyledons of cucumber (Cucumis sativus) seedlings, and increased during greening. The enzyme was present only in the cytosol of the etiolated cotyledons and appeared in the peroxisomes during greening. The enzyme was purified to homogeneity from the cytosol of the etiolated cotyledons and from the peroxisomes of the green cotyledons of cucumber seedlings. The two enzyme preparations had nearly identical enzymic and physical properties. On the basis of these findings, roles of glutamate:glyoxylate aminotransferase in the glycollate pathway in photorespiration, and the mechanism of its appearance in the peroxisomes during greening, are discussed.
