ADP-glucose pyrophosphorylase is located in the plastid in developing tomato fruit

The subcellular location of activity and protein of ADP-glucose pyrophospho rylase (AGPase) in developing tomato (Lycopersicon esculentum) fruit was de termined following a report that the enzyme might be present inside and out side the plastids in this organ. Plastids prepared from crude homogenates o f columella and pericarp, the starch-accumulating tissues of developing fru it, contained 8% to 18% of the total activity of enzymes known to be confin ed to plastids, and 0.2% to 0.5% of the total activity of enzymes known to be confined to the cytosol. The proportion of the total activity of AGPase in the plastids was the same as that of the enzymes known to be confined to the plastid. When samples of plastid and total homogenate fractions were s ubjected to immunoblotting with an antiserum raised to AGPase, most or all of the protein detected was plastidial. Taken as a whole, these data provid e strong evidence that AGPase is confined to the plastids in developing tom ato fruit.