Lysine metabolism in higher plants
ABSTRACT The essential amino acid lysine is synthesised in higher plants via a pathway starting with aspartate, that also leads to the formation of threonine, methionine and isoleucine. Enzyme kinetic studies and the analysis of mutants and transgenic plants that overaccumulate lysine, have indicated that the major site of the regulation of lysine synthesis is at the enzyme dihydrodipicolinate synthase. Despite this tight regulation, there is strong evidence that lysine is also subject to catabolism in plants, specifically in the seed. The two enzymes involved in lysine breakdown, lysine 2-oxoglutarate reductase (also known as lysine a-ketoglutarate reductase) and saccharopine dehydrogenase exist as a single bifunctional protein, with the former activity being regulated by lysine availability, calcium and phosphorylation/ dephosphorylation.
Full-textDOI: · Available from: Ricardo Antunes Azevedo, Jun 27, 2014
- SourceAvailable from: Kimitsune Ishizaki
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- "using the same approach, which revealed that [ 14 C] label fed to barley (Hordeum vulgare) seeds was converted into Glu and a-amino adipic semialdehyde (Sodek and Wilson, 1970; Brandt, 1975). In addition, numerous approaches have been taken to boost the Lys content in plants (Azevedo and Lea, 2001; Galili et al., 2001; Ufaz and Galili, 2008), and for this reason, the degradative pathway has also been targeted. In one such strategy , a series of transgenic maize (Zea mays) plants overaccumulating Lys were produced using distinct strategies, including an endosperm-specific RNA interference suppression of LKR/ SDH (Houmard et al., 2007; Frizzi et al., 2008; Reyes et al., 2009). "
ABSTRACT: The process of dark-induced senescence in plants is relatively poorly understood, but a functional electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) complex, which supports respiration during carbon starvation, has recently been identified. Here, we studied the responses of Arabidopsis thaliana mutants deficient in the expression of isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase to extended darkness and other environmental stresses. Evaluations of the mutant phenotypes following carbon starvation induced by extended darkness identify similarities to those exhibited by mutants of the ETF/ETFQO complex. Metabolic profiling and isotope tracer experimentation revealed that isovaleryl-CoA dehydrogenase is involved in degradation of the branched-chain amino acids, phytol, and Lys, while 2-hydroxyglutarate dehydrogenase is involved exclusively in Lys degradation. These results suggest that isovaleryl-CoA dehydrogenase is the more critical for alternative respiration and that a series of enzymes, including 2-hydroxyglutarate dehydrogenase, plays a role in Lys degradation. Both physiological and metabolic phenotypes of the isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase mutants were not as severe as those observed for mutants of the ETF/ETFQO complex, indicating some functional redundancy of the enzymes within the process. Our results aid in the elucidation of the pathway of plant Lys catabolism and demonstrate that both isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase act as electron donors to the ubiquinol pool via an ETF/ETFQO-mediated route.The Plant Cell 05/2010; 22(5):1549-63. DOI:10.1105/tpc.110.075630 · 9.58 Impact Factor
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- "synthesis in plants. From the 1960s till the 1980s, the biochemistry of the aspartate pathway that leads to lysine synthesis in plant and bacteria was extensively investigated (Azevedo and Lea 2001). The aspartate pathway was revealed to be very complex, frequently with the end product amino acids regulating the activities of key enzymes of the pathway (Azevedo et al. 1997, 2006) (Fig. 2). "
ABSTRACT: Forty-five years ago, a paper published by Mertz et al. (Science 145:279-280, 1964) initiated a revolution in the history of plant protein quality and affected dramatically the study of cereal crop storage proteins. The observation of the high lysine content of the endosperm of the opaque-2 (o2) maize mutant was a key factor in bringing about a new concept in the production of cereal seeds with a high nutritional value. It has been a long and very interesting road with astonishing results over these 45 years. We are now probably about to see the release of commercially engineered high-lysine maize lines. We have decided to pinpoint some key contributions to the science behind high-lysine plants and concentrated on the research done on maize, which is possibly the most complete and simple example to illustrate the advances achieved. However, studies on other plant species such as barley and model species such as tobacco are totally relevant and will be briefly addressed.Amino Acids 04/2010; 39(4):979-89. DOI:10.1007/s00726-010-0576-5 · 3.65 Impact Factor
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- "After some success in producing high-lysine biochemical mutants and transgenic plants expressing altered regulation of lysine biosynthetic enzymes (Azevedo et al., 1990; Shaul and Galili, 1992a, b; 1993; Heremans and Jacobs, 1997; Lee et al., 2001), it became apparent that the rate of lysine breakdown may regulate the amount of lysine that can accumulate in the seed (Azevedo, 2002). Studies with the opaque-2 maize mutant were the most significant ones concerning lysine catabolism, since this mutant is characterized by a high-lysine concentration when compared to wild-type maize seeds, which is due to an altered storage protein distribution and higher accumulation of lysine in the soluble form (Gaziola et al., 1999). "
ABSTRACT: Aspartate is the common precursor of the essential amino acids lysine, threonine, methionine and isoleucine in higher plants. In addition, aspartate may also be converted to asparagine, in a potentially competing reaction. The latest information on the properties of the enzymes involved in the pathways and the genes that encode them is described. An understanding of the overall regulatory control of the flux through the pathways is undisputedly of great interest, since the nutritive value of all cereal and legume crops is reduced due to low concentrations of at least one of the aspartate-derived amino acids. We have reviewed the recent literature and discussed in this paper possible methods by which the concentrations of the limiting amino acids may be increased in the seeds.Amino Acids 04/2006; 30(2):143-62. DOI:10.1007/s00726-005-0245-2 · 3.65 Impact Factor