Valine Metabolism in Arabidopsis
Branched-chain amino acids (BCAAs) are essential amino acids, meaning mammals have the inability to synthesize them de novo and must therefore obtain them through dietary intake. They have been well studied in mammalian systems due to their key role in several metabolic and signaling pathways. Plants, on the other hand, have the ability to synthesize and degrade BCAAs, although the metabolism and importance of these amino acids is less well understood. It is known that mutations in the biosynthetic pathway results in herbicide resistant plants, whereas mutations in the degradation pathway result in an array of responses, from resistance to hormones, to embryo lethality. The largest questions concerning BCAA metabolism in plants involve understanding valine and propionyl-CoA metabolic pathways. It is believed they share a common pathway; however, the localization and actual enzymatic reactions remain controversial. In an effort to piece together this pathway, several techniques were employed. NMR spectroscopic results showed the peroxisomal metabolism of exogenous propionate through a pathway similar to valine degradation in the mitochondria. Reverse genetics using several knockout mutants in the valine degradation pathway, as well as measuring mRNA levels under several stress conditions, helped to resolve much of the ambiguity regarding this pathway. Based on the data presented in this dissertation, we are the first to provide evidence for the metabolism of propionyl-CoA by a modified ?-oxidation pathway that utilizes both the mitochondria and the peroxisomes to produce acetyl-CoA. In addition, preliminary data are presented regarding the maintenance of BCAA homeostasis and evidence for the stimulation of protein synthesis.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:valine metabolism arabidopsis propionyl coa hydroxyisobutyryl hydrolase methylmalonate semialdehyde dehydrogenase and leucine
Date of Publication:01/01/2008