The physiological role of malic enzyme in grape ripening
- Cite this article as:
- Ruffner, H.P., Possner, D., Brem, S. et al. Planta (1984) 160: 444. doi:10.1007/BF00429761
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The high specificity of malic enzyme (ME; EC 126.96.36.199) from grape berries (Vitis vinifera L.) for the naturally occurring l-enantiomer of malic acid, its very selective C4-decarboxylation, and certain allosteric properties, reported previously, favour the conjecture of a regulatory function of ME in fruit malic acid degradation. On the other hand, high ME activity was detected even during the acid-accumulating phase of berry development. Also, the in vitro reversibility of the reaction supports the possibility of malate formation under conditions facilitating carboxylation of pyruvate, notably high CO2/HCO3-and NADPH/NADP ratios. However, a very limited incorporation of 14C into malate and the uniform labeling pattern of the dicarboxylic acid after administration of [U-14C] alanine to grape berries before and after the onset of ripening, indicate that the ‘reverse” reaction does not contribute essentially to grape malate synthesis. A regulatory mechanism mediating malic acid remetabolization on the basis of cosubstrate availability, comparable to the control of the hexose monophosphate shunt, is discussed.
Key wordsFruit ripeningMalic enzymeVitis (fruit ripening)
Malic enzyme (l-malate: NADP oxidoreductase)