Retrobiosynthetic nuclear magnetic resonance analysis of amino acid biosynthesis and intermediary metabolism. Metabolic flux in developing maize kernels
E. Glawischnig et al., Retrobiosynthetic nuclear magnetic resonance analysis of amino acid biosynthesis and intermediary metabolism. Metabolic flux in developing maize kernels, PLANT PHYSL, 125(3), 2001, pp. 1178-1186
Information on metabolic networks could provide the basis for the design of
targets for metabolic engineering. To study metabolic flux in cereals, dev
eloping maize (Zea mays) kernels were grown in sterile culture on medium co
ntaining [U-C-13(6)]glucose or [1,2-C-13(2)]acetate. After growth, amino ac
ids, lipids, and sitosterol were isolated from kernels as well as from the
cabs, and their C-13 isotopomer compositions were determined by quantitativ
e nuclear magnetic resonance spectroscopy. The highly specific labeling pat
terns were used to analyze the metabolic pathways leading to amino acids an
d the triterpene on a quantitative basis. The data show that serine is gene
rated from phosphoglycerate as well as from glycine. Lysine is formed entir
ely via the diaminopimelate pathway and sitosterol is synthesized entirely
via the mevalonate route. The labeling data of amino acids and sitosterol w
ere used to reconstruct the labeling patterns of key metabolic intermediate
s (e.g. acetyl-coenzyme A, pyruvate, phosphoenolpyruvate, erythrose 4-phosp
hate, and Rib 5-phosphate) that revealed quantitative information about car
bon nux m the intermediary metabolism or developing maize Kernels. Exogenou
s acetate served as an efficient precursor of sitosterol, as well as of ami
no acids of the aspartate and glutamate family; in comparison, metabolites
formed in the plastidic compartments showed low acetate incorporation.