Malate valves: old shuttles with new perspectives

Autor(en): Selinski, J.
Scheibe, R. 
Stichwörter: AMINO-ACID; ATP/ADP TRANSPORTERS; BACTERIAL EXPRESSION; CO2 FIXATION; CRUCIAL ROLE; Energy supply; malate dehydrogenase; malate valve; MITOCHONDRIAL METABOLISM; MOLECULAR CHARACTERIZATION; OXIDATIVE STRESS; Plant Sciences; PLASTIDIAL GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE; redox balance; REDOX REGULATION; shuttling
Erscheinungsdatum: 2019
Herausgeber: WILEY
Journal: PLANT BIOLOGY
Volumen: 21
Ausgabe: 1, SI
Startseite: 21
Seitenende: 30
Zusammenfassung: 
Malate valves act as powerful systems for balancing the ATP/NAD(P)H ratio required in various subcellular compartments in plant cells. As components of malate valves, isoforms of malate dehydrogenases (MDHs) and dicarboxylate translocators catalyse the reversible interconversion of malate and oxaloacetate and their transport. Depending on the co-enzyme specificity of the MDH isoforms, either NADH or NADPH can be transported indirectly. Arabidopsis thaliana possesses nine genes encoding MDH isoenzymes. Activities of NAD-dependent MDHs have been detected in mitochondria, peroxisomes, cytosol and plastids. In addition, chloroplasts possess a NADP-dependent MDH isoform. The NADP-MDH as part of the `light malate valve' plays an important role as a poising mechanism to adjust the ATP/NADPH ratio in the stroma. Its activity is strictly regulated by post-translational redox-modification mediated via the ferredoxin-thioredoxin system and fine control via the NADP(+)/NADP(H) ratio, thereby maintaining redox homeostasis under changing conditions. In contrast, the plastid NAD-MDH ('dark malate valve') is constitutively active and its lack leads to failure in early embryo development. While redox regulation of the main cytosolic MDH isoform has been shown, knowledge about regulation of the other two cytosolic MDHs as well as NAD-MDH isoforms from peroxisomes and mitochondria is still lacking. Knockout mutants lacking the isoforms from chloroplasts, mitochondria and peroxisomes have been characterised, but not much is known about cytosolic NAD-MDH isoforms and their role in planta. This review updates the current knowledge on MDH isoforms and the shuttle systems for intercompartmental dicarboxylate exchange, focusing on the various metabolic functions of these valves.
ISSN: 14358603
DOI: 10.1111/plb.12869

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