Plasmalemma-associated malate dehydrogenase activity in onion root cells |
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Authors: | M C Córdoba-Pedregosa J A González-Reyes A Serrano J M Villalba P Navas F Córdoba |
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Institution: | (1) Present address: Departamento de Biología Celular, Facultad de Ciencias, Universidad de Córdoba, Avda. San Alberto Magno s/n, E-14004 Córdoba, Spain;(2) Departamento de Economía y Empresa, Universidad Pablo de Olavide , Sevilla;(3) Departamento de Ciencias Agroforestales, Universidad de Huelva, Huelva |
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Abstract: | Summary Plasma membrane vesicles isolated from onion roots showed oxaloacetate reductase activity as well as other oxidoreductase activities. Purification and further sequencing showed that the protein responsible for the activity is a 40 kDa protein which corresponds to the cytosolic soluble malate dehydrogenase. However, the activity remained bound to the membrane after repeated freezing and thawing cycles and further washing, excluding a cytosolic contamination as the source of the activity. Furthermore, a second 28 kDa protein has been copurified together with the 40 kDa protein. The plasmalemma oxaloacetate reductase activity shows both donor and acceptor sites located towards the cytoplasmic side of the plasma membrane. This enzyme catalyzed the oxidation of NADH by oxaloacetate and the reduction of NAD+ by malate in the presence of an oxaloacetate-withdrawing system. We conclude that a significant amount of the cytosolic malate dehydrogenase can be specifically attached to the cytosolic face of the plasmalemma. A possible role in a putative malate shuttle associated to the plasma membrane is discussed.Abbreviations AFR
ascorbate free radical
- DQ
duroquinone
- OA
oxaloacetate
- DPIP
dichlorophenolindophenol
- MDH
malate dehydrogenase
- PHMB
p-hydroxymercuribenzoate |
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Keywords: | Allium cepa L Malate dehydrogenase root Plasma membrane |
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