The control of NAD specific malic enzyme from cauliflower bud mitochondria by metabolites
✍ Scribed by D. D. Davies; K. D. Patil
- Book ID
- 104751059
- Publisher
- Springer-Verlag
- Year
- 1975
- Tongue
- English
- Weight
- 767 KB
- Volume
- 126
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
NAD malic enzyme (EC. 1.1.1.39) has been purified from cauliflower (Brassica oleracea, var. botrytis) bud mitochondria. The enzyme exhibits complex regulatory properties being activated by a variety of metabolites including glyeolytic intermediates, CoA, sulphate and Krebs cycle acids--the triearboxylic acids with the exception of citrate being more effective than dicarboxylie acids. Fructose diphosphate which is a positive effector of the enzyme increases the affinity of the enzyme for L-malate.
The enzyme is inhibited by glutamate, aspartate, phosphate and ATP, in the latter case the inhibition is largely due to chelation of Mg 2+. The plot of rate versus malate concentration is sigmoid at pH 7.0 with Mg 2+ but normal Michaelis-lVienten kinetics are observed with Mn 2+. The molecular weight of the enzyme as measured by gel filtration is ca. 400000. The physiological significance of the responses to metabolites is discussed. Andrews (1965) using liver alcohol dehydrogenase, lactate dehydrogenase and glueose-6-phosphate dehydrogenase as markers on a Sephadcx G-200 column.
Decarboxylation o/ Malate by Intact Mitochondria. The decarboxylation of malate and fumarate was measured using a C02 electrode as described by Nicholls et al. (1967). The release of 14C02 from malate-l,4-14C was measured as described by Davies and Corbctt (1969).