Gloeocapsa UTEX sp. LB 795, like other blue-green algae, was found to lack a functional citric acid cycle. This is probably due to the absence of an enzyme capable of oxidising 2-oxoglutarate to succinate. The significance of the incomplete citric acid cycle, particularly the conversion of acetate to 2-oxoglutarate, is discussed in terms of the provision of carbon skeletons for ammonia assimilation and the provision of reducing power for nitrogen fixation. It is concluded that the activity of isocitrate dehydrogenase is probably not sufficient on its own to provide all the reducing power for nitrogen fixation in vivo. A number of alternative oxidoreductases were examined and their activities measured at different stages of growth of the culture and compared to the activity of nitrogenase at the same stages of growth. These results are discussed in terms of the provision of reducing power for nitrogenase. In particular, glucose-6-phosphate dehydrogenase is suggested as being able to meet the requirement for nitrogen fixation. The assimilation of t4C-labelled citrate, glutamate, malate and pyruvate was found to be extremely slow, probably due to their inabillty to penetrate the cell membrane. The turnover of endogenously C-labelled intermediates was measured and the results discussed in terms of the rate of flow of carbon through various metabolic pathways. The intracellular concentration of NAD was found to be much lower than that of NADP and this finding is used to explain the apparent slow rate of interconversion of malate and oxaloacetate. The contribution of the various metabolic pathways to the provision of reducing power for nitrogenase is discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637367 |
| Date | January 1978 |
| Creators | Ikram-Ul-Haque, C. M. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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