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- De Koning, Tom J., et al.
(författare)
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Amino Acid Synthesis Deficiencies
- 2022. - 2
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Ingår i: Physician's Guide to the Diagnosis, Treatment, and Follow-Up of Inherited Metabolic Diseases, Second Edition. - Cham : Springer International Publishing. - 9783030721848 - 9783030721831 ; , s. 453-467
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Bokkapitel (refereegranskat)abstract
- In recent years the list of disorders affecting amino acid synthesis has grown rapidly. Not only the number of defects has increased, but also the associated clinical phenotypes have expanded spectacular, the latter mainly due to the advances of next-generation sequencing diagnostics. An important reason for the contribution of NGS in the diagnosis of amino acid synthesis disorders is the fact that the biochemical diagnosis of some of these synthesis disorders can be quite challenging, synthesis defects may present with low values of amino acids, or their concentrations can even be completely normal. Defects in the synthesis pathways of serine metabolism, glutamine, glutamate, proline, and asparagine have been reported, and all pose specific challenges to a biochemical diagnosis. An exception to this are the disorders of pyrroline-5-carboxylate (P5C) synthesis where ornithine or proline is strongly elevated and easily detected by plasma amino acid analysis. Finally, Snyder-Robinson, a defect in the synthesis of the polyamine spermine, is discussed here as well, and molecular testing is advised for this disorder as well. Although the amino acid synthesis defects in this chapter are not all in related metabolic pathways, they do share some clinical features. In children the central nervous system is primarily affected, giving rise to (congenital) microcephaly, early-onset seizures, and mental retardation to a variable degree. The brain abnormalities can be accompanied by skin disorders such as cutis laxa in proline defects, collodion-like skin and ichthyosis in serine deficiency, necrolytic erythema in glutamine deficiency, and difficult to classify skin abnormalities in glutaminase hyperactivity. In adults with serine or proline disorders, several forms of polyneuropathy with or without intellectual disability appear to be the major presenting symptom. An exception to this is ornithine aminotransferase deficiency which primarily affects the choroid and retina and Snyder-Robinson syndrome in which mental retardation is accompanied by seizures, dysmorphic features, and severe osteoporosis.
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| 4. |
- Zimmermann, Sandra E., et al.
(författare)
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The phosphorylated pathway of serine biosynthesis links plant growth with nitrogen metabolism
- 2021
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Ingår i: Plant Physiology. - : Oxford University Press. - 0032-0889 .- 1532-2548. ; 186:3, s. 1487-1506
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Tidskriftsartikel (refereegranskat)abstract
- Because it is the precursor for various essential cellular components, the amino acid serine is indispensable for every living organism. In plants, serine is synthesized by two major pathways: photorespiration and the phosphorylated pathway of serine biosynthesis (PPSB). However, the importance of these pathways in providing serine for plant development is not fully understood. In this study, we examine the relative contributions of photorespiration and PPSB to providing serine for growth and metabolism in the C3 model plant Arabidopsis thaliana. Our analyses of cell proliferation and elongation reveal that PPSB-derived serine is indispensable for plant growth and its loss cannot be compensated by photorespiratory serine biosynthesis. Using isotope labeling, we show that PPSB-deficiency impairs the synthesis of proteins and purine nucleotides in plants. Furthermore, deficiency in PPSB-mediated serine biosynthesis leads to a strong accumulation of metabolites related to nitrogen metabolism. This result corroborates N-15-isotope labeling in which we observed an increased enrichment in labeled amino acids in PPSB-deficient plants. Expression studies indicate that elevated ammonium uptake and higher glutamine synthetase/glutamine oxoglutarate aminotransferase (GS/GOGAT) activity causes this phenotype. Metabolic analyses further show that elevated nitrogen assimilation and reduced amino acid turnover into proteins and nucleotides are the most likely driving forces for changes in respiratory metabolism and amino acid catabolism in PPSB-deficient plants. Accordingly, we conclude that even though photorespiration generates high amounts of serine in plants, PPSB-derived serine is more important for plant growth and its deficiency triggers the induction of nitrogen assimilation, most likely as an amino acid starvation response.
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