Die Glucose-6-phosphat Dehydrogenase im Stoffwechsel photoautotropher Organismen

Abstract

Summary Glucose-6-phosphate dehydrogenase is an especially important agent in regulating the flux of carbon through the oxidative pentose phosphate pathway. Separate species of the enzyme occur in chloroplasts and cytoplasm. There is a strong competition for glucose-6-phosphate between oxidative pentose phosphate pathway and glycolysis. Glucose-6-phosphate is also a key intermediate for generation of additional NADPH + H + , for providing the carbon skeleton for cell wall components, and also for a variety of aromatic and phenolic compounds. The kinetics, the influence of effectors, as well as multiple forms and isoenzymes of glucose-6-phosphate dehydrogenase are probably of importance for the extent of metabolism of glucose-6-phosphate following one of these pathways. Photomodulation regulates the activity between the reductive and oxidative pentose phosphate pathway in chloroplasts (in connection with the NADPH + H + /NADP + ratio). There is tremendous variation in the distribution of the enzyme in plant tissues, depending on plant-species, growth conditions and developmental stages. Especially the presence of isoenzymes and multiple forms of glucose-6-phosphate dehydrogenase in plant cells raises problems which are still open until now.