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| DC Field | Value | Language |
|---|---|---|
| dc.contributor.advisor | Aidil Abdul Hamid, Prof. Dr. | - |
| dc.contributor.author | Zangoma Maryam Haladu (P80378) | - |
| dc.date.accessioned | 2023-09-25T09:34:24Z | - |
| dc.date.available | 2023-09-25T09:34:24Z | - |
| dc.date.issued | 2018-03 | - |
| dc.identifier.other | ukmvital:101666 | - |
| dc.identifier.uri | https://ptsldigital.ukm.my/jspui/handle/123456789/463690 | - |
| dc.description | Malic enzyme (ME) and NAD⁺: dependent isocitrate dehydrogenase (NAD⁺: ICDH) are two major enzymes known to play an important role in lipid biosynthesis of oleaginous microorganisms. This study attempts to investigate the role of ME and its isoforms as well as NAD⁺: ICDH in the regulation of lipid accumulation in Aurantiochytrium sp. SW1. The phase at which lipid accumulation begins was investigated, and the role of ME and its isoforms as well as NAD⁺: ICDH were studied in relation to growth and lipid accumulation. The microalga was grown in Burja medium for 120 h at 30 °C and 200 rpm in shake flasks (250 mL) and also by fermentation in a 5 L bioreactor. The growth and lipid content of the microalgae were observed throughout the cultivation period. The active growth phase of this microalga in both the shake flasks and bioreactor occurred until 48 h and the growth rate slowed down at 72 h coincident with nitrogen depletion. Lipid synthesis started during the active growth phase in the presence of nitrogen with up to 20 % lipid (g/g biomass) accumulated at 24 h and achieved 35 % at 48 h, indicating that the lipid accumulation of this organism is growth-related. Up to 68 % lipid (g/g biomass) was accumulated at 96 h with an increase in lipid productivity observed after N depletion compared to growth phase, indicating the importance of nitrogen limited condition in lipid accumulation of the microalgae. When the activities of lipogenic enzymes such as fatty acid synthase (FAS), ATP: citrate lyase (ACL) and NADPH-producing enzymes ME, glucose 6-phosphate dehydrogenase (G-6PDH), 6-phosphoglutanate dehydrogenase (6-PGDH), and NADP⁺: ICDH were assayed, high specific activities of ME, FAS and ACL were observed beginning at 24 h, coincided with the beginning of lipid synthesis in the growth phase. The activities significantly decreased at 96 h along with the cessation of lipid accumulation. The NADPH producing enzymes G-6PDH, 6-PGDH and ME showed correlation with lipid accumulation with percentage reductions of 46, 45 and 43 % respectively in their activities followed by the reduction in lipid content at 72 h. This indicates that these enzymes are equally important in the regulation of lipid accumulation in Aurantiochytrium sp. SW1 during growth phase while the increase in activity of NADP⁺: ICDH suggested it to be important during post growth phase. Furthermore, the role of ME in lipid accumulation was investigated by inhibiting its activity with sesamol. Results showed that the addition of 4 mM sesamol resulted in 67 % reduction in ME specific activity which affected biomass concentration and lipid content achieved (75 % and 44 % reduction, respectively). This indicates that ME activity is involved in both growth and lipid synthesis of Aurantiochytrium sp. SW1. When ME isoforms were assayed using native PAGE, results showed that ME exists in eight isoforms namely isoforms A, B, C, D, E, F, G and H. The correlation of isoform D (approximately 160 kDa) to lipid accumulation during growth phase was indicated by the distinct presence of the 160 kDa molecule between 24 to 48 h which eventually ceased to be detected during post growth phase (72 h to 96 h), coincident with decrease in ME specific activity. The presence of isoform D only in 24 and 48 h culture and its complete disappearance in 72 and 96 h cultures upon inhibition of ME with sesamol further supports its involvement in lipid accumulation of Aurantiochytrium sp. SW1 during growth phase. The activity of NAD⁺: ICDH was present throughout the cultivation period with a slight decrease in its activity with the onset of lipid accumulation. In vitro test on the effect of AMP on the activity showed that unlike previously reported in yeasts, the enzyme has no dependency on AMP for its activity. These differences and its implication in the regulation of lipid accumulation is further discussed.,“Certification of Master's/Doctoral Thesis” is not available,Master of Science | - |
| dc.language.iso | eng | - |
| dc.publisher | UKM, Bangi | - |
| dc.relation | Faculty of Science and Technology / Fakulti Sains dan Teknologi | - |
| dc.rights | UKM | - |
| dc.subject | Lipid | - |
| dc.subject | Microalgae | - |
| dc.subject | Enzymes | - |
| dc.title | The role of malic enzyme (ME) and NAD⁺: isocitrate dehydrogenase (NAD: ICDH) in lipid biosynthesis of Aurantiochytrium sp. SWI | - |
| dc.type | theses | - |
| dc.format.pages | 98 | - |
| dc.identifier.callno | QP601.H258 2017 tesis | - |
| dc.identifier.barcode | 003531(2018) | - |
| Appears in Collections: | Faculty of Science and Technology / Fakulti Sains dan Teknologi | |
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|---|---|---|---|---|
| ukmvital_101666+SOURCE1+SOURCE1.0.PDF Restricted Access | 876.77 kB | Adobe PDF |  View/Open |
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