[Carbon dioxide fixation and its regulation in Synechococcus (Anacystis nidulans) cyanobacteria]

The bulk of 14CO2 assimilated in photosynthesis by the growing culture of Synechococcus was incorporated in the cell via the reductive pentose phosphate cycle. Up to 70% of the label was incorporated into phosphoglyceric acid and phosphoric esters of sugars at all stages of the active cultural growth after 1 min of exposition in the light in the presence of NaH14CO3. The relative proportion of the label in phosphorylated compounds of the reductive pentose phosphate cycle decreased if the exposition was increased to 20 min. The content of 14C in aspartic acid did not exceed 9%. In the presence of nucleotide peptide (NP) isolated from Anabaena variabilis, the overall rate of carbon dioxide assimilation rised by 50% as compared to the control by the fourth day of the growth. The specific rate of 14CO2 assimilation hardly changed within four days of the cultural growth; it was 44 nmole/min/mg, or 55 nmole/min/mg in the presence of NP. NP had no effect on the qualitative composition of the products of photosynthesis; however, the percentage of sugar phosphates, phosphoenolpyruvate and organic acids (carbohydrates at the stage of exponential growth) in these products increased in the presence of NP (exposition for 20 min). The percentage of carbohydrates was found to change only slightly as compared to the control in the presence of NP. The content of protein and RNA increased by 25-30% and the content of DNA by 60%. The action of NP was most pronounced if the content of DNA was calculated per cell. Therefore, there is a correlation between the content of DNA and the intensification of carbon dioxide fixation by the culture.