Carbohydrate breakdown by chloroplasts of Pisum sativum.

1. The aims of this work were to discover the pathways of starch breakdown and carbohydrate metabolism in intact isolated chloroplasts from shoots of Pisum sativum. 2. 14C from starch, labelled by supplying [14C]glucose to chloroplasts, appeared, during starch breakdown, in CO2, maltose and the fraction of the acidic compounds that contained 3-phosphoglycerate and sugar phosphates. 3. When intact chloroplasts were incubated in the dark, 3-phosphoglycerate, triose phosphates and, to a lesser extent, hexose 6-phosphates accumulated in the medium at rates comparable to those of starch breakdown in leaves. This accumulation was dependent upon orthophosphate. 4. The patterns of 14CO2 production from specifically labelled [14C]glucose supplied to isolated chloroplasts were those expected of the oxidative pentose phosphate pathway with extensive recycling, and glycolysis. The respone of this pattern to lack of orthophosphate, addition of unlabelled intermediates, and 2-phosphoglycollate confirmed this view. 5. Starch breakdown in pea chloroplasts is held to be dominantly phosphorolytic with the products being metabolized via the oxidative pentose phosphate pathway and glycolysis to 3-phosphoglycerate, triose phosphates and CO2 that are exported to the cytoplasm.