Malate carboxy lyase

The role that the malo-lactic reaction—the decarboxylation of malic acid—plays in the overall physiology of the cell, and the enzymatic pathway of the reaction are two questions which have plagued enologists since the discovery of the reaction. Morenzoni (71) has described this discovery by Ochoa and coworkers (72, 73, 74), and he has related how their early representation of the reaction led to some confusion. We are now convinced, from studies by Radler and coworkers (75, 76) with partly purified enzymes from Lactobacillus and Leuconostoc, that the reaction is catalyzed by an inducible malate carboxy lyase with NAD (nicotinamide adenine dinucleotide) and Mn2+ as cofactors ... 

NADH as an end product. This implicates oxidized malic acid, either pyruvic or oxaloacetic acid, as another end product. By adding commercial preparations of L-lactic dehydrogenase or malic dehydrogenase to the reaction mixture, Morenzoni (90) concluded that the end product was pyruvic acid. Attempts were then made to show whether two enzymes—malate carboxy lyase and the classic malic enzyme, malate oxidoreductase (decarboxylating), were involved or if the two activities were on the same enzyme. The preponderance of evidence indicated that only one enzyme is involved. This evidence came from temperature inactivation studies, heavy-metal inhibition studies, and ratio measurements of the two activities of partially purified preparations of Schiitz and Radlers malo-lactic enzyme (76, 90). This is not the first case of a single enzyme having two different activities (91). 

Our work (6, 7, 8) has shown that the same protein which causes the malic acid-lactic acid transformation will also cause the production of a small amount of pyruvic acid from malic acid. However, the pyruvic acid produced is not involved with lactic acid production. Apparently, one protein is producing two end products from the same substrate. The malic acid to lactic acid activity is not an oxidoreductase whereas the malic acid to pyruvic acid activity is. Since the pyruvic acid producing activity is only a small per cent (about 0.2%) of the malic acid to lactic acid activity, and since the enzyme should be classified according to the major end product, the enzyme has been given the trivial frame of malo-lactic enzyme (6, 7, 8). Schiitz (28) has speculated that if this enzyme were crystallized, it should be called malate-carboxy-lyase. In either case, use of either the trivial or accepted terms for the malic enzyme is not recommended. 

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See also in sourсe #XX -- [ ]

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