Starch phosphorylase isoenzymes in mesophyll and bundle sheath cells of corn leaves

Starch phosphorylase from leaves of the C₄-plant corn (Zea mays L.) could be separated into two peaks of activity by chromatography on DEAE-cellulose (or by (NH₄)₂SO₄ gradient solubilization). Subsequent polyacrylamide gel electrophoresis under native conditions revealed a slowly migrating phosphorylase for the peak eluting first from DEAE-cellulose and a major, fast migrating phosphorylase for the peak eluting second. The latter peak contained also two very minor bands which migrated even faster than the other two phosphorylases. When phosphorylases were extracted from mesophyll protoplasts and from bundle sheath strands (isolated by the enzymatic isolation procedure) it was the slowly migrating phosphorylase which was associated with the mesophyll cells and the major, fast migrating phosphorylase which originated from the bundle sheath cells. The findings are discussed in view of similar isoenzymes of phosphorylase reported for chloroplasts and cytosol in leaves of C₃-plants.