The cytosolic pathway of L-malic acid synthesis in Saccharomyces cerevisiae: the role of fumarase.
Saccharomyces cerevisiae accumulates L-malic acid but not only minute amounts of fumaric acid. A 13C-nuclear magnetic resonance study following the label from glucose to L-malic acid indicates that the L-malic acid is synthesized from pyruvic acid via oxaloacetic acid. From this, and from previously published studies, we conclude that a cytosolic reductive pathway leading from pyruvic acid via oxaloacetic acid to L-malic acid is responsible for the L-malic acid production in yeast. The non-production of fumaric acid can be explained by the conclusion that, in the cell, cytosolic fumarase catalyzes the conversion of fumaric acid to L-malic but not the reverse. This conclusion is based on the following findings. (a) The cytosolic enzyme exhibits a 17-fold higher affinity towards fumaric acid than towards L-malic acid; the Km for L-malic acid is very high indicating that L-malic acid is not an in vivo substrate of the enzyme. (b) Overexpression of cytosolic fumarase does not cause accumulation of fumaric acid (but rather more L-malic acid). (c) According to 13C NMR studies there is no interconversion of cytosolic L-malic and fumaric acids.
Pines
O
O
Department of Molecular Biology, Hebrew University-Hadassah Medical School, Jerusalem, Israel. ophry@md2.huji.ac.il
Even-Ram
S
S
Elnathan
N
N
Battat
E
E
Aharonov
O
O
Gibson
D
D
Goldberg
I
I
D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002952:Citric Acid Cycle / Q000502:physiology; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism*; D005649:Fumarate Hydratase / Q000235:genetics / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008293:Malates / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology; D010071:Oxaloacetates / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000378:metabolism*; D013379:Substrate Specificity
D007476:Ionophores; D008293:Malates; D010071:Oxaloacetates; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; C030298:malic acid; D019289:Pyruvic Acid; D005649:Fumarate Hydratase