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A pre-genetic study of the isoforms of malic enzyme associated with lipid accumulation in Mucor circinelloides

Centre for Advanced Lipid Research, Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK¹

Author for correspondence: James P. Wynn. Tel: +44 1482 465507. Fax: +44 1482 465458. e-mail: j.p.wynn{at}biosci.hull.ac.uk

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 O₂-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.

Keywords: isoforms, continuous culture, filamentous fungi

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				Y. Zhang, I. P. Adams, and C. Ratledge Malic enzyme: the controlling activity for lipid production? Overexpression of malic enzyme in Mucor circinelloides leads to a 2.5-fold increase in lipid accumulation Microbiology, July 1, 2007; 153(7): 2013 - 2025. [Abstract] [Full Text] [PDF]