Glycolysis is the main metabolic route in Saccharomyces cerevisiae and it is the sequence of enzyme catalyzed reactions that oxidatively convert glucose to pyruvic acid in the yeast cytoplasm. In addition to the basic steps, glycolysis involves branch points providing the intermediary building blocks of the cell (i.e amino acids and nucleotides). One of these pathways is glucose-6-phosphate branch point which is a junction of glycolytic pathway and pentose phosphate pathway. At this point glucose-6-phosphate can be converted to fructose-6-phosphate a metabolite of glycolytic pathway by phosphoglucoisomerase or it can be dehydrogenated to 6-phosphogluconolactone by glucose-6-phosphate dehydrogenase which is the first enzyme of the pentose phosphate pathway.
In this study, the influence of different nitrogen sources on the flux distribution through the pentose phosphate pathway and glycolysis in Saccharomyces cerevisiae was examined. For this purpose, four different compositions of nitrogen sources were used in growth media. The growth medium contained one of the following composition of nitrogen sources / only ammonium sulfate, only yeast nitrogen base, ammonium sulfate and histidine, yeast nitrogen base and histidine. Histidine was added because its synthesis branches from pentose phosphate pathway. In order to analyse the effect of the different compositions of nitrogen sources on the physiology of the yeast, specific activities of hexokinase, phosphoglucose isomerase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase enzymes were measured in the crude extracts of the biomass samples taken in the late exponential phase of the cultures.
Addition of histidine caused an increase in the specific activities of all the enzymes analysed in medium containing ammonium sulfate. The specific activity of hexokinase, phosphoglucose isomerase and glucose-6-phosphate dehydrogenase in medium containing yeast nitrogen base and histidine were higher than medium containing yeast nitrogen base. However, the specific activity of 6-phosphogluconate dehydrogenase decreased 3.1% in medium containing yeast nitrogen base and histidine medium with respect to medium with only yeast nitrogen base.
The OD value and dry weight in the culture containing histidine aminoacid was higher than the cultures contaning only ammonium sulfate and only yeast nitrogen base. Also the period of the exponential phase was shorter in medium containing ammonium sulfate and histidine and yeast nitrogen base and histidine than medium only ammonium sulfate and only yeast nitrogen base.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12606556/index.pdf |
| Date | 01 October 2005 |
| Creators | Alagoz, Eda |
| Contributors | Hamamci, Haluk |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
Page generated in 0.0063 seconds