ADP-glucose pyrophosphorylase (ACP) was purified from tomato (Lycopersicon esculentum Mill.) fruit to apparent homogeneity. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis the enzyme migrated as two close bands with molecular weights of 50,000 and 51,000. Two-dimensional polyacrylamide gel electrophoresis analysis of the purified enzyme, however, revealed at least five major protein spots that could be distinguished by their slight differences i n net charge and molecular weight. Whereas all of the spots were recognized by the antiserum raised against tomato fruit ACP holoenzyme, only three of them reacted strongly with the antiserum raised against the potato tuber ACP large subunit, and the other two spots (with lower molecular weights) reacted specifically with antisera raised against spinach leaf ACP holoenzyme and the potato tuber ACP small subunit. l h e results suggest the existente of at least three isoforms of the ACP large subunit and two isoforms of the small subunit in tomato fruit in vivo. The native molecular mass of the enzyme determined by gel filtration was 220 f 1 O kD, indicating a tetrameric structure for ACP from tomato fruit. l h e purified enzyme is very sensitive to 3-phosphoglycerate/ inorganic phosphate regulation.

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