Occurrence of phosphorylating and non-phosphorylating NADP +-dependent glyceraldehyde-3-phosphate dehydrogenases in photosynthetic organisms

Abstract

A survey of the occurrence of the NADP +-dependent, phosphorylating and non-phosphorylating, glyceraldehyde-3-phosphate dehydrogenases (G3P DHases) in different microalgae and higher plants has been performed. The phosphorylating G3P DHase (EC 1.2.1.13), a typical photosynthetic enzyme, was found in all types of algae examined and in the photosynthetic tissues of higher plants (C3, C4 and Crassulacean species). The non-phosphorylating G3P DHase (EC 1.2.1.9) was also present in eukaryotic microalgae, higher plants and Cyanophora paradoxa, but was not detected in either prokaryotic blue-green algae or non-photosynthetic microorganisms. In plants, the activity level of the non-phosphorylating enzyme was higher in photosynthetic tissues than in roots, the phosphorylating activity being absent from roots. The occurrence of the non-phosphorylating G3P DHase seems, therefore, a specific feature of those organisms with chloroplasts or cyanelles. This agrees with the proposed function for this enzyme in photosynthesis as a component of an export system of both reducing power and protons from the chloroplast stroma to the cytosol.