Nicotinamide Adenine Dinucleotide-specific “Malic” Enzyme in Kalanchoë daigremontiana and Other Plants Exhibiting Crassulacean Acid Metabolism
- 1 February 1976
- journal article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 57 (2), 310-314
- https://doi.org/10.1104/pp.57.2.310
Abstract
NAD-specific “malic” enzyme (EC 1.1.1.39) has been isolated and purified 1200-fold from leaves of Kalanchoë daigremontiana. Kinetic studies of this enzyme, which is activated 14-fold by CoA, acetyl-CoA, and SO42−, suggest allosteric properties. Cofactor requirements show an absolute specificity for NAD and for Mn2+, which cannot be replaced by NADP or Mg2+. For maintaining enzyme activity in crude leaf extracts a thiol reagent, Mn2+, and PVP-40 were required. The latter could be omitted from purified preparations. By sucrose density gradient centrifugation NAD-malic enzyme could be localized in mitochondria. A survey of plants with crassulacean acid metabolism revealed the presence of NAD-malic enzyme in all 31 plants tested. Substantial levels of this enzyme (121-186 μmole/hr·mg of Chl) were detected in all members tested of the family Crassulaceae. It is proposed that NAD-malic enzyme in general supplements activity of NADP-malic enzyme present in these plants and may be specifically employed to increase internal concentrations of CO2 for recycling during cessation of gas exchange in periods of severe drought.Keywords
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