A pre-genetic study of the isoforms of malic enzyme associated with lipid accumulation in Mucor circinelloides.
The oleaginous fungus Mucor circinelloides possesses at least six isoforms of malic enzyme (EC 1.1.1.40), a key lipogenic enzyme in filamentous fungi. These isoforms were detected using a specific stain for activity after native PAGE of cell extracts. Only one isoform (isoform IV) was associated with lipid accumulation, appearing only after N-exhaustion from the medium (which is a pre-requisite for lipid accumulation) in glucose-growing cells. Isoforms I, II, V and VI were involved in anaerobic growth and only appeared under O(2)-limited conditions. Isoform III appeared to be constitutive and was formed under conditions of active (balanced) growth and is therefore thought to play a crucial role in basic metabolism. Growth on acetate increased the amount of cell lipid (from 25-27% in glucose-grown cells to 37-38% in acetate-grown cells) accumulated by M. circinelloides and this was associated with the appearance of isoform IV of malic enzyme prior to N-exhaustion in these cultures. Amino acid sequence analysis of isoforms III and IV suggests that these two malic enzymes may be encoded by a single gene and that isoform IV is formed from isoform III by post-translational modification initiated by either N-limitation (when glucose was the carbon source) or growth on acetate as the sole carbon source.
Song
Yuanda
Y
Centre for Advanced Lipid Research, Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK1.
Wynn
James P
JP
Centre for Advanced Lipid Research, Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK1.
Li
Yonghua
Y
Centre for Advanced Lipid Research, Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK1.
Grantham
David
D
Centre for Advanced Lipid Research, Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK1.
Ratledge
Colin
C
Centre for Advanced Lipid Research, Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK1.
D000085:Acetates / Q000378:metabolism; D000693:Anaerobiosis; D003470:Culture Media; D004591:Electrophoresis, Polyacrylamide Gel; D005947:Glucose / Q000378:metabolism; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism; D050356:Lipid Metabolism; D008291:Malate Dehydrogenase / Q000302:isolation & purification / Q000378:metabolism*; D009089:Mucor / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism; D020539:Sequence Analysis, Protein
D000085:Acetates; D003470:Culture Media; D007527:Isoenzymes; D008291:Malate Dehydrogenase; C046446:malate dehydrogenase-(oxaloacetate-decarboxylating) (NAD+); C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); D005947:Glucose