Ribulose-1,5-bisphosphate carboxylase in the bundle sheath cells of maize leaf1

By employing the one-step enzymic digestion of maize leaf tissues, mesophyll protoplasts and bundle sheath strands were separated without cross-contamination. Ribulose-1,5-bisphosphate (RuP2 carboxylase and NADP-malic enzyme were found to be exclusively localized in the bundle sheath cells, whereas phosphoenolpyruvate carboxylase, the primary carboxylation enzyme in the C4-photosynthetic pathway, was only present in the mesophyll cells. Immunochemical precipitation experiments using the rabbit antisera developed against the spinach leaf RuP2 carboxylase revealed the entire absence of this enzyme protein and/or immunologically related molecules in the mesophyll cells. The structural relatedness of the maize carboxylase molecule with the spinach enzyme, containing the large (A) and small (B) subunits was demonstrated, and from the quantitative immunoassay it was estimated that the enzyme protein comprises at least 30% of the total soluble protein in the bundle sheath cells.