Partial Purification and Characterization of Ribulose-1,5bisphosphate carboxylase from the Developing Endosperm Tissue of Zea mays L.

Abstract

Summary Ribulose-1,5-bisphosphate carboxylase/oxygenase was present in the developing endosperm of maize (Zea mays L.). The enzyme was detected by the RuBP dependent fixation of NaHC03. A substantial portion of the enzymic activity was located in the proplastid fraction, as identified by the marker enzymes triosephosphate isomerase and triosephosphate dehydrogenase. The specific activity of Rubisco in crude extracts of endosperm 10 to 15 days postpollination was approximately 6 nmoles C02 fixed min- I mg-1 protein. The activity could be purified 20 fold by precipitation with ammonium sulfate followed by chromatography on Sepharose 4B and DEAE cellulose. The enzyme preparation had a major protein band on 7.5 % polyacrylamide disc gel electrophoresis which corresponded to that of crystalline tobacco Rubisco. After polyacrylamide disc gel electrophoresis in the presence of SDS, bands were seen at 5.5 x 104 and 1.2 x 104 daltons, suggesting that the enzyme has a quaternary structure identical to that of the enzyme from other higher plants. A metabolic function for this enzyme in this tissue is unlikely in light of its low specific activity and the high activity of PEP carboxylase.