Decarboxylation of Malate in the Crassulacean Acid Metabolism Plant Bryophyllum (Kalanchoe) fedtschenkoi (Role of NAD-Malic Enzyme)

Abstract

The role of NAD-malic enzyme (NAD-ME) in the Crassulacean acid metabolism plant Bryophyllum (Kalanchoe) fedtschenkoi was investigated using preparations of intact and solubilized mitochondria from fully expanded leaves. Intact, coupled mitochondria isolated during the day or night did not differ in their ability t o take up ['4Clmalic acid from the surrounding medium or to respire using malate or succinate as substrate. However, intact mitochondria isolated from plants during the day decarboxylated added malate to pyruvate significantly faster than mitochondria isolated from plants at night. NAD-ME activity i n solubilized mitochondrial extracts showed hysteretic kinetics and was stimulated by a number of activators, including acetyl-coenzyme A, fructose-I ,6-bisphosphate, and sulfate ions. I n the absence of these effectors, reaction progress curves were nonlinear, with a pronounced acceleration phase. The lag period before a steady-state rate was reached in assays of mitochondrial extracts decreased during the photoperiod and increased slowly during the period of darkness. However, these changes in the kinetic properties of the enzyme could not account for the changes in the rate of decarboxylation of malate by intact mitochondria. Cel-filtration experiments showed that mitochondrial extracts contained three forms of NAD-ME with different molecular weights. The relative proportions of the three forms varied somewhat throughout the light/dark cycle, but this did not account for the changes i n the kinetics behavior of the enzyme during the diurna1 cycle.

Species variation in the intracellular localization of pyruvate, Pi dikinase in leaves of crassulacean-acid-metabolism plants: an immunogold electron-microscope study

“…In K. daigremontiana, the increase in CAM activity during leaf development is associated not only with an increase in NAD-ME activity but also a decline in NADP-ME activity . In KalanchoeÈ fedtschenkoi (Cyt-Chlt), the mitochondria isolated during the day decarboxylate malate to pyruvate more rapidly than those isolated at night, and the kinetic properties of NAD-ME dier between day and night (Cook et al 1995). These data suggest that in the KalanchoeÈ species, NAD-ME plays a signi®cant role in malate decarboxylation.…”

Intracellular transport and pathways of carbon flow in plants with crassulacean acid metabolism

“…NAD-ME may therefore act as a decarboxylase during the dark. Indeed, there is little evidence for the day-night regulation of activity of this enzyme (Cook et al 1995). It is possible that one function of the increase in NAD-ME activities observed following the induction of CAM in M. crystallinum might be related to maintaining a pyruvate supply at night in the mitochondria.…”

Transgenic Perturbation of the Decarboxylation Phase of Crassulacean Acid Metabolism Alters Physiology and Metabolism But Has Only a Small Effect on Growth

“…Although understanding of the regulation of primary nocturnal CO 2 fixation by PPC is relatively well developed, malate decarboxylation and the subsequent light-period steps of CAM, and their regulation, are less well studied, even in physiologically and biochemically well-studied constitutive/obligate CAM species such as Kalanchoë fedtschenkoi (Cook et al, 1995). High activities of both mitochondrial NAD-ME and chloroplastic/ cytosolic NADP-ME have been detected in leaf extracts of various ME-type CAM species (Dittrich, 1976;Spalding et al, 1979;Christopher and Holtum, 1996), but the relative importance of the two forms of ME to malate decarboxylation in the light period during CAM is poorly understood.…”