Methods for studying plant transketolases

This chapter describes methods of purification and biochemical characterization of plant transketolases. The methods have been developed initially for transketolase from the desiccation tolerant plant Craterostigma plantagineum. Like other plants, C. plantagineum encodes several isoforms of transketolase. The main isoform represents a key enzyme in the pentose phosphate cycle and in photosynthesis where it catalyzes the synthesis of sugar phosphates. Other isoforms synthesize rare sugar phosphates such as octulose-phosphate. This demonstrates that besides primary metabolism, transketolases in plants may be involved in the synthesis of species-specific sugar metabolites. If the identity of the sugar is not known, a combination of gas chromatography and mass spectrometry need to be applied for the identification. The different isoforms of transketolase can be localized in different cellular compartments, such as plastids and cytoplasm. Experimental strategies are described to demonstrate the subcellular localization of transketolases.