Identification and characterisation of the alpha and beta subunits of succinyl CoA ligase of tomato.
Despite the central importance of the TCA cycle in plant metabolism not all of the genes encoding its constituent enzymes have been functionally identified. In yeast, the heterodimeric protein succinyl CoA ligase is encoded for by two single-copy genes. Here we report the isolation of two tomato cDNAs coding for alpha- and one coding for the beta-subunit of succinyl CoA ligase. These three cDNAs were used to complement the respective Saccharomyces cerevisiae mutants deficient in the alpha- and beta-subunit, demonstrating that they encode functionally active polypeptides. The genes encoding for the subunits were expressed in all tissues, but most strongly in floral and leaf tissues, with equivalent expression of the two alpha-subunit genes being expressed to equivalent levels in all tissues. In all instances GFP fusion expression studies confirmed an expected mitochondrial location of the proteins encoded. Following the development of a novel assay to measure succinyl CoA ligase activity, in the direction of succinate formation, the evaluation of the maximal catalytic activities of the enzyme in a range of tissues revealed that these paralleled those of mRNA levels. We also utilized this assay to perform a preliminary characterisation of the regulatory properties of the enzyme suggesting allosteric control of this enzyme which may regulate flux through the TCA cycle in a manner consistent with its position therein.
Studart-Guimarães
Claudia
C
Max-Planck Institute for Molecular Plant Physiology, Am Mühlenberg 1, 14476 Golm, Germany.
Gibon
Yves
Y
Frankel
Nicolás
N
Wood
Craig C
CC
Zanor
María Inés
MI
Fernie
Alisdair R
AR
Carrari
Fernando
F
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D018551:Solanum lycopersicum / Q000166:cytology / Q000201:enzymology*; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013389:Succinate-CoA Ligases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D019802:Succinic Acid / Q000378:metabolism
D021122:Protein Subunits; D019802:Succinic Acid; D013389:Succinate-CoA Ligases