MULTIPLE FORMS OF ADP-GLUCOSE PYROPHOSPHORYLASE FROM TOMATO FRUIT

ADP-glucose pyrophosphorylase (ACP) was purified from tomato (Lycopers icon esculentum Mill.) fruit to apparent homogeneity. By sodium dodecy l sulfate-polyacrylamide gel electrophoresis the enzyme migrated as tw o close bands with molecular weights of 50,000 and 51,000. Two-dimensi onal polyacrylamide gel electrophoresis analysis of the purified enzym e, however, revealed at least five major protein spots that could be d istinguished by their slight differences in net charge and molecular w eight. Whereas all of the spots were recognized by the antiserum raise d against tomato fruit AGP holoenzyme, only three of them reacted stro ngly with the antiserum raised against the potato tuber ACP large subu nit, and the other two spots (with lower molecular weights) reacted sp ecifically with antisera raised against spinach leaf AGP holoenzyme an d the potato tuber AGP small subunit. The results suggest the existenc e of at least three isoforms of the AGP large subunit and two isoforms of the small subunit in tomato fruit in vivo. The native molecular ma ss of the enzyme determined by gel filtration was 220+/-10 kD, indicat ing a tetrameric structure for ACP from tomato fruit. The purified enz yme is very sensitive to 3-phosphoglycerate/inorganic phosphate regula tion.