ISSN:
1432-2048
Keywords:
Fruit ripening
;
Malic enzyme
;
Vitis (fruit ripening)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The high specificity of malic enzyme (ME; EC 1.1.1.40) 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/HCO 3 - 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00429761
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