The Enzymatic Role of Lipid Metabolism in Yarrowia lipolytica Grown on Glycerol

More attention has been paid to the production of commercial fatty acids by microbial fermentation. The basic biochemistry of lipid accumulation in oleaginous microorganisms under nitrogen limitation has been extensively studied. As an oleaginous microorganism, Yarrowia lipolytica can produce fatty acid-derived biofuels and biochemicals. However, the response of the enzymes in Y. lipolytica to glycerol remains unclear. Therefore, we aimed to identify the rate-limiting enzymes associated with the mechanism of lipid accumulation of Y. lipolytica grown on glycerol. The variations in key enzyme activities of fatty acid accumulation in Y. lipolytica were investigated with glycerol as the single carbon source. The nitrogen source was exhausted at 10 h in the medium, leading to substantial changes in key enzyme activities associated with lipid accumulation. Adenosine monophosphate deaminase activity increased immediately by approximately twofold. NAD⁺-isocitrate dehydrogenase activity decreased by 65% after the nitrogen source was exhausted when compared to the initial maximum activity. ATP citrate lyase activity, which provides the substrate acetyl coenzyme A for lipid biosynthesis, increased by approximately fourfold when compared to the activity before nitrogen depletion. Malic Enzyme (ME) activity decreased considerably after nitrogen was exhausted so that the reducing power Nicotinamide Adenine Dinucleotide Phosphate (NADPH) required for lipid synthesis cannot be produced by ME. However, glucose-6-phosphate dehydrogenase activity increased from 550 nmol·min^-1·mg^-1-771 nmol·min^-1·mg^-1, suggesting that the main source of NADPH required for fatty acid accumulation may be provided by the pentose phosphate pathway when Y. lipolytica grew on the medium with glycerol as the only carbon source.