Abstract

Metabolism of 2-carboxyarabinitol 1-phosphate (CA 1-P), an endogenous inhibitor of ribulose bisphosphate carboxylase/oxygenase, occurs in the light. A soluble protein fraction which metabolized CA 1-P in the presence of NADPH was isolated from tobacco chloroplasts. A similar fraction from spinach exhibited much lower activity. The activity in tobacco extracts was stable overnight at 4°C but its maintenance during storage required dithiothreitol. The tobacco protein responsible for CA 1-P metabolism was partially purified by ion-exchange FPLC of stromal extracts. The requirements for NADPH and dithiothreitol for activity of this protein suggest a mechanism for the light-dependent control of CA 1-P levels in plants.

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