The role of malic enzyme in the regulation of lipid accumulation in filamentous fungi.
The hypothesis is advanced that NADP(+)-malic enzyme (ME; EC 1.1.1.40) is an important activity in regulating the extent of lipid accumulation in filamentous fungi. In Mucor circinelloides, a fungus capable of accumulating only 25% (w/w, dry wt) lipid, even under the most propitious conditions, ME disappears 15-20 h after nitrogen exhaustion, coincident with the cessation of lipid accumulation. In contrast, ME in Mortierella alpina, a fungus capable of accumulating 50% (w/w, dry wt) lipid, remains active for over 60 h after N-exhaustion during which time lipid accumulation continues. No other enzyme activity studied, including the lipogenic enzymes acetyl-CoA carboxylase, fatty acid synthase, diacyglycerol acyltransferase, ATP: citrate lyase and the NADPH-generating enzymes glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and NADP+:isocitrate dehydrogenase, demonstrated any correlation with the accumulation of storage lipid in either fungus. Full activity of ME is restored in Mr. circinelloides within 4 h by adding NH4+ to the cultures, but this is prevented by adding cycloheximide as an inhibitor of protein synthesis. This suggests that the decrease in ME activity occurs due to down-regulation of the ME gene.
Wynn
James P
JP
Hamid
Aidil Bin Abdul
ABA
Ratledge
Colin
C
D003470:Culture Media; D015966:Gene Expression Regulation, Fungal; D050356:Lipid Metabolism; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D020094:Mortierella / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism; D009089:Mucor / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism
D003470:Culture Media; D008293:Malates; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+)