[C4-Pathway of photosynthesis in the blue-green alga Anacystis nidulans].

CO2 exchange, (14)CO2 fixation and radioactive photosynthetic products of Anacystis nidulans (strain L 1402-1) were studied during the induction period at +30° C. The algae were grown at +35° C in an atmosphere of 0.03 or 3.0 vol.-% CO2 and were measured under conditions of low CO2 concentrations. At the beginning of the photosynthetic period (14)CO2 was mainly incorporated into aspartate and glutamate. The patterns of labelling are very similar to those of the C4 pathway of photosynthesis. α-Hydroxypyridylmethane-sulfonic acid (10(-5) M) and isonicotinyl hydrazide (10(-2) M) have only a small effect on the percentage distribution of labelled products. The activities of glycolate dehydrogenase, ribulose-1,5-diphosphate carboxylase and phosphoenolpyruvate carboxylase, measured in crude extracts of Anacystis, were inhibited by α-hydroxypyridylmethane-sulfonic acid and dichlorophenyldimethyl urea.In other series of experiments the pattern of (14)C incorporation from asparate was investigated. Radioactivity from [(14)C]aspartate was mainly incorporated into glutamate, alanine, theronine, isoleucine and glycine/serine. Enzyme activities of citrate synthase, aconitate hydratase, isocitrate dehydrogenase and glutamate dehydrogenase were relatively low in CO2-grown Anacystis cells compared to those in air grown cells. The obtained results are discussed, with reference to the operation of the C4 pathway of photosynthesis and reductive carboxylation of succinate to glutamate in Anacystis.