influence of metal ions on malic enzyme activity and lipid synthesis in Aspergillus niger

• Published in: FEMS microbiology letters Vol. 217; no. 2; pp. 185 - 190
• Main Authors: Jernejc, K, Legisa, M
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 17.12.2002; Blackwell; Oxford University Press
• Subjects: Adenine; Aspergillus niger; Aspergillus niger - drug effects; Aspergillus niger - enzymology; Aspergillus niger - metabolism; Binding sites; Biological and medical sciences; Biosynthesis; Cations - pharmacology; Citric acid; Citric Acid - analysis; Copper; Copper - pharmacology; Copper ion; Enzymatic activity; Enzyme activity; enzyme inhibition; Enzymes; Fundamental and applied biological sciences. Psychology; Growth, nutrition, metabolism, transports, enzymes. Molecular biology; Ions; Iron; Kinetics; Lipids; Lipids - adverse effects; Lipids - analysis; Lipids - biosynthesis; Magnesium; Malate Dehydrogenase - metabolism; Malic enzyme; Manganese; Metal concentrations; Metal inhibition; Metal ions; Metals - pharmacology; Microbiology; Mycology; NADP (coenzyme); NADPH-diaphorase; Nicotinamide; Nicotinamide adenine dinucleotide; Overflow; Zinc; Lipids; Copper ion; Metal inhibition; Malic enzyme; Citric acid; Enzyme; Metal ion; Environmental factor; ); Biosynthesis; Malate dehydrogenase (oxaloacetate-decarboxylating) (NADP; Fungi; Enzymatic activity; Aspergillus niger; Fungi Imperfecti; Oxidoreductases; Copper; Thallophyta
• ISSN: 0378-1097; 1574-6968
• DOI: 10.1111/j.1574-6968.2002.tb11473.x

In the presence of copper significant induction of citric acid overflow was observed, while concomitantly lower levels of total lipids were detected in the cells. Its effect was more obvious in a medium with magnesium as sole divalent metal ions, while in a medium with magnesium and manganese the addition of copper had a less pronounced effect. Since the malic enzyme was recognised as a supplier of reducing power in the form of reduced nicotinamide adenine dinucleotide phosphate for lipid biosynthesis, its kinetic parameters with regard to different concentrations of metal ions were investigated. Some inhibition was found with Fe(2+) and Zn(2+), while Cu(2+) ions in a concentration of 0.1 mM completely abolished malic enzyme activity. The same metal ions proportionally reduced the levels of total lipids in Aspergillus niger cells. A strong competitive inhibition of the enzyme by Cu(2+) was observed. It seemed that copper competes with Mg(2+) and Mn(2+) for the same binding site on the protein.