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PubMed1994

Hysteresis of cytosolic NADP-malic enzyme II from Trypanosoma cruzi.

NADP-malic enzyme II, one of two isoenzymes of NADP-malic enzyme (EC 1.1.1.40) in Trypanosoma cruzi epimastigotes, presents hysteretic behavior that results in a kinetic lag in the reaction progress curve. The lag is affected by the malate, aspartate and oxaloacetate concentrations in the assay mixture. This dependence suggests that hysteresis is due to an association-dissociation process influenced by the binding of these ligands to the enzyme. The enzyme was separated from NADP-malic enzyme I and purified 43-fold from a cell homogenate by a procedure involving column chromatography on DEAE-Sephacel and Cibacron-blue Sepharose. The molecular mass of the highly purified enzyme was determined as 126 kDa.

Animals↗

PubMed1988

Purification and characterization of NADP+-linked isocitrate dehydrogenase from an alkalophilic Bacillus.

We have succeeded in purifying to homogeneity a very labile NADP+-linked isocitrate dehydrogenase (isocitrate: NADP+ oxidoreductase (decarboxylating), EC 1.1.1.42) from a strain of alkalophilic Bacillus, by a simple method, with an overall yield over 76% of the original activity. The molecular weight on Sephadex G-200 was around 90,000; and that by electrophoresis on SDS-polyacrylamide gels was about 44,000. The sedimentation coefficient (s020,w) and isoelectric point of the enzyme were determined to be 3.22 S and pH 4.7, respectively. The enzyme required Mn2+ for the reaction and for stability. The optimum pH for the reaction was in the range 7.8-8.4 at 30 degrees C; the optimum temperature at pH 8.0 was 75 degrees C; the activation energy of the reaction was 6.2 kcal/mol. The Km values for threo-Ds-isocitrate, DL-isocitrate, and NADP+ were 5.4 microM, 9.9 microM, and 7.3 microM, respectively. This enzyme was inhibited by NADPH, glyceraldehyde 3-phosphate, 3-phosphoglycerate, phosphoenol pyruvate, cis-aconitate, alpha-ketoglutarate, and oxaloacetate. In addition, it was subject to a concerted inhibition by a combination of glyoxylate and oxaloacetate, and also to a cumulative inhibition by nucleoside triphosphates.

Bacillus↗

PubMed1978

The effect of phenobarbitone on cytoplasmic NADP-linked dehydrogenase activities in rat liver.

Phenobarbitone administered in drinking water (0.5 g/l) or by daily intraperitoneal injection (100 mg/kg body weight) consistently caused an elevation of hepatic NADP-linked malic enzyme in rats maintained on a pellet diet. Three to four days appeared to be required for maximum response. The effect was also observed in animals maintained on a protein rich diet, in which the basic hepatic malic enzyme activity was low, but not in animals maintained on a sucrose rich diet, in which the basic enzyme activity was almost twice normal. Methyl cholanthrene, administered by daily intraperitoneal injection (40 mg/kg body weight), resulted in elevated hepatic levels not only of malic enzyme but also of the pentose phosphate pathway dehydrogenases. The timing of the "starve-refeed" response of the hepatic NADP-linked dehydrogenases in phenobarbitone-treated rats was similar to that in controls, and similar maximum enzyme activities were reached. The role of cytoplasmic NADP-linked dehydrogenases in the provision of reducing equivalent is discussed, particularly in relation to hepatic microsomal drug metabolism.

Animals↗

PubMed1988

Isotope effect studies of the chemical mechanism of pig heart NADP isocitrate dehydrogenase.

The catalytic mechanism of porcine heart NADP isocitrate dehydrogenase has been investigated by use of the variation of deuterium and 13C kinetic isotope effects with pH. The observed 13C isotope effect on V/K for isocitrate increases from 1.0028 at neutral pH to a limiting value of 1.040 at low pH. The limiting 13C isotope effect with deuteriated isocitrate at low pH is 1.016. This decrease in 13(V/KIc) upon deuteriation indicates a stepwise mechanism for the oxidation and decarboxylation of isocitrate. This predicts a deuterium isotope effect on V/K of 2.9, but D(V/K) at low pH only increases to a maximum of 1.08. It is not known why 13(V/KIc) with deuteriated isocitrate decreases more than predicted. The pK seen in the 13(V/KIc) pH profile for isocitrate is 4.5. This pK is displaced 1.2 pH units from the true pK of the acid/base functionality of 5.7 seen in the pKi profile for oxalylglycine, a competitive inhibitor for isocitrate. From this displacement, catalysis is estimated to be 16 times faster than substrate dissociation. By use of the pH-dependent partitioning ratio of the reaction intermediate oxalosuccinate between decarboxylation to 2-ketoglutarate and reduction to isocitrate, the forward commitment to catalysis for decarboxylation was determined to be 7.3 at pH 5.4 and 3.2 at pH 5.0. This gives an intrinsic 13C isotope effect for decarboxylation of 1.050. 3-Fluoroisocitrate is a new substrate oxidatively decarboxylated by NADP isocitrate dehydrogenase. At neutral pH, D(V/K3-F-Ic) = 1.45 and 13(V/K3-F-Ic) = 1.0129. At pH 5.2, 13(V/K3-F-Ic) increases to 1.0186, indicating that a finite, but diminished, external commitment remains at neutral pH. The product of oxidative decarboxylation of 3-hydroxyisocitrate by NADP isocitrate dehydrogenase is 2-hydroxy-3-ketoglutarate. This results from enzymatic protonation of the cis-enediol intermediate at C2 rather than C3 (as seen with isocitrate and 3-fluoroisocitrate). 2-Hydroxy-3-ketoglutarate further decarboxylates in solution to 2-hydroxy-3-ketobutyrate, which further decarboxylates to acetol. This makes 3-hydroxyisocitrate unsuitable for 13C isotope effect studies.

Animals↗

PubMed2002

Intrasteric inhibition in redox signalling: light activation of NADP-malate dehydrogenase.

Chloroplast NADP-dependent malate dehydrogenase (NADP-MDH, EC 1.1.1.82) is inactive in the dark and activated in the light via a reduction of specific disulfides by thiol-disulfide interchange with thioredoxin, reduced by the photosynthetic electron transfer. Compared to the constitutively active NAD-dependent forms, NADP-MDH exhibits two regulatory disulfides per subunit, one located in an N-terminal extension and the other in a C-terminal extension. Convergent information gathered from biochemical, site-directed mutagenesis and structural approaches allowed to solve almost completely the activation mechanism. In the oxidized enzyme, the C-terminal extension is pulled back by the disulfide bridge toward the active-site cleft where the penultimate C-terminal glutamate interacts with one of the arginines involved in substrate binding, thus acting as an internal inhibitor obstructing the access of oxaloacetate. The N-terminal extensions are located at the subunit interface area and rigidify the overall structure of the dimer. Their reduction by reduced thioredoxin triggers a conformational change of the active site towards high-activity conformation, whereas the reduction of the C-terminal bridge expells the C-terminal end from the active site, thus opening the way for the substrate.

Journal Article↗

PubMed1999

Distribution of two isoforms of NADP-dependent isocitrate dehydrogenase in soybean (Glycine max).

Two different cDNAs that encode NADP-specific isocitrate dehydrogenase (NADP-IDH) isozymes of soybean (Glycine max) were characterized. The nucleotide sequences of the coding regions of these cDNAs have 74% identity to each other and give predicted amino acid sequences that have 83% identity to each other. Using PCR techniques, their coding regions were subcloned into a protein overexpression vector, pQE32, to yield pIDH4 and pIDH1, respectively. Both IDH4 and IDH1 enzymes were expressed in Escherichia coli as catalytically active His6 tagged proteins, purified to homogeneity by affinity chromatography on nickel chelate resin and rabbit polyclonal antibodies to each were generated. Surprisingly, antiserum to IDH4 did not react with IDH1 protein and IDH1 antiserum reacted only very weakly with IDH4 protein. IDH4 antibody reacts with a protein of expected molecular weight in cotyledon, young leaf, young root, mature root and nodules but the reaction with mature leaf tissue was low compared to other tissues. Western blot results show that IDH1 was not expressed in young roots but a protein that reacts with the IDH1 antibody was highly expressed in leaves, showing that there was tissue-specific accumulation of NADP-IDH isozymes in soybean.

Antibody Specificity↗

PubMed1986

NADP-specific isocitrate dehydrogenase from the citric acid-accumulating fungus Aspergillus niger.

NADP-specific isocitrate dehydrogenase [threo-DS-isocitrate: NADP+ oxidoreductase (decarboxylating), EC 1.1.1.42] was purified 200-300-fold from the citric acid-accumulating fungus Aspergillus niger. The enzyme consists of a single polypeptide chain with a molecular mass of 60 +/- 4 kDa and has a pI of 5.9 +/- 0.2. Only a single enzyme protein was found, although the enzyme appears to occur both in the mitochondrion and in the cytoplasm. Growth on organic acids as carbon sources or on NO3- as nitrogen source led to increased activities, whereas the presence of amino acids led to lower activities. The enzyme exhibits hyperbolic kinetics with respect to its substrates isocitrate and NADP+. Mn2+ and Mg2+ are obligatory for enzyme activity. The enzyme is inhibited by its products alpha-oxoglutarate and NADPH. Among various metabolites, ATP and citrate appear to inhibit the enzyme at a concentration considered to occur intracellularly. In both cases, however, the mechanism is a removal of the metal ion cofactor from the substrates. It is concluded that under physiological conditions, where the Mg2+ content is around 10 mM, the observed inhibition by ATP or citrate is of poor regulatory significance.

Aspergillus niger↗

PubMed2002

Crystal structure of porcine mitochondrial NADP+-dependent isocitrate dehydrogenase complexed with Mn2+ and isocitrate. Insights into the enzyme mechanism.

The crystal structure of porcine heart mitochondrial NADP+-dependent isocitrate dehydrogenase (IDH) complexed with Mn2+ and isocitrate was solved to a resolution of 1.85 A. The enzyme was expressed in Escherichia coli, purified as a fusion protein with maltose binding protein, and cleaved with thrombin to yield homogeneous enzyme. The structure was determined by multiwavelength anomalous diffraction phasing using selenium substitution in the form of selenomethionine as the anomalous scatterer. The porcine NADP+-IDH enzyme is structurally compared with the previously solved structures of IDH from E. coli and Bacillus subtilis that share 16 and 17% identity, respectively, with the mammalian enzyme. The porcine enzyme has a protein fold similar to the bacterial IDH structures with each monomer folding into two domains. However, considerable differences exist between the bacterial and mammalian forms of IDH in regions connecting core secondary structure. Based on the alignment of sequence and structure among the porcine, E. coli, and B. subtilis IDH, a putative phosphorylation site has been identified for the mammalian enzyme. The active site, including the bound Mn2+-isocitrate complex, is highly ordered and, therefore, mechanistically informative. The consensus IDH mechanism predicts that the Mn2+-bound hydroxyl of isocitrate is deprotonated prior to its NADP+-dependent oxidation. The present crystal structure has an active site water that is well positioned to accept the proton and ultimately transfer the proton to solvent through an additional bound water.

Amino Acid Sequence↗

PubMed2003

Critical role of Lys212 and Tyr140 in porcine NADP-dependent isocitrate dehydrogenase.

Lys212 and Tyr140 are close to the enzyme-bound isocitrate in the recently determined crystal structure of porcine NADP-specific isocitrate dehydrogenase (Ceccarelli, C., Grodsky, N. B., Ariyaratne, N., Colman, R. F., and Bahnson, B. J. (2002) J. Biol. Chem. 277, 43454-43462). We have constructed mutant enzymes in which Lys212 is replaced by Gln, Tyr, and Arg, and Tyr140 is replaced by Phe, Thr, Glu, and Lys. Wild type and mutant enzymes were each expressed in Escherichia coli and purified to homogeneity. At pH 7.4, the specific activity is decreased in K212Q, K212Y, and K212R, respectively, to 0.01-9% of wild type. The most striking change is in the pH-V(max) curves. Wild type depends on the deprotonated form of a group of pKaes 5.7, whereas this pKaes is increased to 7.4 in neutral K212Q and to 8.3 in K212Y. In contrast, the positive K212R has a pKaes of 5.9. These results indicate that (by electrostatic repulsion) a positively charged residue at position 212 lowers the pK of the nearby ionizable group in the enzyme-substrate complex. Lys212 may also stabilize the carbanion formed initially on substrate decarboxylation. The Tyr140 mutants have specific activities at pH 7.4 that are reduced to 0.2-0.5% of those of wild type, whereas their Km values for isocitrate and NADP are not increased. Most notable are the altered pH-V(max) profiles. V(max) is constant from pH 5.3 to 8 for Y140F and Y140T and increases as pH is decreased for Y140E and Y140K. These results suggest that in wild type enzyme, Tyr140 is the general acid that protonates the substrate after decarboxylation and that the carboxyl and ammonium forms of Y140E and Y140K provide partial substitutes. Relative to wild type, the Y140T enzyme is specifically activated 106-fold by exogenous addition of acetic acid and 88-fold by added phenol; and the K212Q enzyme is activated 4-fold by added ethylamine. These chemical rescue experiments support the conclusion that Tyr140 and Lys212 are required for the catalytic activity of porcine NADP-dependent isocitrate dehydrogenase.

Animals↗

PubMed1991

Kinetics of induction of cytosolic benzaldehyde: NADP and propionaldehyde: NAD aldehyde dehydrogenase activities in rat livers from male Wistar rats.

The time courses of induction of liver cytosolic aldehyde dehydrogenases using benzaldehyde and propionaldehyde as substrates and NADP and NAD as co-factors after i.p. and intragastric (i.g.) administration of 2-acetylaminofluorene (2-AAF), 20-methylcholanthrene (20-MC), beta-naphthoflavone (beta-NF) and benzo[alpha]pyrene (B[alpha]P) were investigated in male Wistar rats. 2-AAF did not induce the aldehyde dehydrogenase activities with any substrate:co-factor combination. The other three inducers all induced the oxidation of the aldehydes in a reversible manner. With an i.p. route of administration (one daily dose for four consecutive days) (20-MC) was the most potent inducer giving a 240-fold increase of benzaldehyde: NADP activity on the ninth day. beta-NF elevated the activity 20-fold with peak activity at day 7, while B[alpha]P gave maximal induction on day 5 with a 60-fold increase in activity over the corresponding value for normal liver. The i.g. administration resulted in a weaker but coordinated induction of activity with peak activity on the sixth day for the different inducers. The activity ratio benzaldehyde:NADP/propionaldehyde:NAD, 0.78 in normal rats, was altered in all induced states to a level close to 4. The interpretation of our work supports the hypothesis that the inducers in this respect use the same mechanisms of induction. The differences noted can be explained by variations in the exposure of the liver to the administered dose and/or by differences in receptor affinity. The inducibility of benzaldehyde:NADP aldehyde dehydrogenase in rat liver exceeds by orders of magnitude the ability of the same inducers to increase the amount of the activity of other drug metabolizing enzymes such as glutathione S-transferase, cytochrome P450 and cytochrome b5. The reversible, drug-dependent induction characterized in normal rat liver in this work differs entirely from the persistent constitutive elevation of the same enzymes in preneoplastic liver nodules.

2-Acetylaminofluorene↗

PubMed1997

Isolation of cDNA for an NADP-malic enzyme from Aloe arborescens.

NADP-malic enzyme catalyzes the reaction of decarboxylation from malate. In CAM plants, functions of this enzyme diverged to include both photosynthetic and non-photosynthetic roles. A full length cDNA for an NADP-malic enzyme was isolated from an 'obligate' CAM plant aloe (Aloe arborescens). The cDNA contains an ORF encoding 592 amino acid residues, whose sequence is highly homologous to the known plant NADP-malic enzymes. This gene is constitutively expressed in all organs in a low level. The amount of the transcript exhibited no diurnal variation, suggesting that this gene is not involved in photosynthetic functions.

Aloe↗

PubMed1997

An NADP-glutamate dehydrogenase from the green alga Bryopsis maxima. Purification and properties.

NADP-glutamate dehydrogenase (EC 1.4.1.4:NADP-GDH) was purified to electrophoretic homogeneity from the multinuclear-unicellular green marine alga in Siphomales, Bryopsis maxima, and its properties were examined. M(r) of the undenatured enzyme was 280 kDa, and the enzyme is thought to be a hexamer of 46 kDa subunit protein. Optimum pHs for the reductive amination and oxidative deamination were 7.5 and 8.2-9.0 respectively. The enzyme displayed NADPH/NADH-specific activities with a ratio of 18:1. Apparent K(m) values for 2-oxoglutarate, ammonia, NADPH, glutamate and NADP+ were 3.0, 2.2, 0.03, 3.2 and 0.01 mM respectively. The enzymochemical characteristics of the GDH were studied and compared to those of other species. The B. maxima GDH was insensitive to 5 mM Ca(2+) and to 1 mM EDTA in contrast to higher plant NAD-GDHs. Chemical modifications with DTNB and pCMBS suggested that cysteine residues are essential for the enzymatic activity as in other species GDHs. The GDH was not affected by 1 mM purine nucleotides, suggesting that the enzyme is not allosteric, in contrast to animal NAD(P)-GDHs and fungal NAD-GDHs.

Amino Acid Sequence↗

PubMed1987

NADP-specific isocitrate dehydrogenase of Mycobacterium phlei ATCC 354: purification and characterization.

NADP-dependent isocitrate dehydrogenase (EC 1.1.1.42) from Mycobacterium phlei ATCC 354 was purified to homogeneity by ammonium sulphate fractionation, followed by DEAE cellulose and Sephadex G-200 chromatography. The pH optimum of the enzyme was 8.5. The Km values for isocitrate and NADP were 74 and 53 microM, respectively. Mn2+ was essential for enzyme activity. The enzyme lost all activity on incubation at 70 degrees C for 15 min; isocitrate and NADP protected against this thermal inactivation. p-Chloromercuribenzoate inhibited the enzyme; pre-incubation of enzyme with isocitrate + Mn2+ prevented this inhibition. The purified enzyme showed concerted inhibition by glyoxylate + oxaloacetate and was inhibited by oxalomalate.

Glyoxylates↗

PubMed1992

Degree of C(4) Photosynthesis in C(4) and C(3)-C(4)Flaveria Species and Their Hybrids : I. CO(2) Assimilation and Metabolism and Activities of Phosphoenolpyruvate Carboxylase and NADP-Malic Enzyme.

The degree of C(4) photosynthesis was assessed in four hybrids among C(4), C(4)-like, and C(3)-C(4) species in the genus Flaveria using (14)C labeling, CO(2) exchange, (13)C discrimination, and C(4) enzyme activities. The hybrids incorporated from 57 to 88% of the (14)C assimilated in a 10-s exposure into C(4) acids compared with 26% for the C(3)-C(4) species Flaveria linearis, 91% for the C(4) species Flaveria trinervia, and 87% for the C(4)-like Flaveria brownii. Those plants with high percentages of (14)C initially fixed into C(4) acids also metabolized the C(4) acids quickly, and the percentage of (14)C in 3-phosphoglyceric acid plus sugar phosphates increased for at least a 30-s exposure to (12)CO(2). This indicated a high degree of coordination between the carbon accumulation and reduction phases of the C(4) and C(3) cycles. Synthesis and metabolism of C(4) acids by the species and their hybrids were highly and linearly correlated with discrimination against (13)C. The relationship of (13)C discrimination or (14)C metabolism to O(2) inhibition of photosynthesis was curvilinear, changing more rapidly at C(4)-like values of (14)C metabolism and (13)C discrimination. Incorporation of initial (14)C into C(4) acids showed a biphasic increase with increased activities of phosphoenolpyruvate carboxylase and NADP-malic enzyme (steep at low activities), but turnover of C(4) acids was linearly related to NADP-malic enzyme activity. Several other traits were closely related to the in vitro activity of NADP-malic enzyme but not phosphoenolpyruvate carboxylase. The data indicate that the hybrids have variable degrees of C(4) photosynthesis but that the carbon accumulation and reduction portions of the C(4) and C(3) cycles are well coordinated.

Journal Article↗

PubMed1976

Events Surrounding the Early Development of Euglena Chloroplasts: VII. Photocontrol of the Source Of Reducing Power for Chloramphenicol Reduction by the Ferredoxin-NADP Reductase System.

d(-)threo-Chloramphenicol blocks chlorophyll and plastid protein synthesis in Euglena. During chloroplast development in white light, but not in red, the cells escape from chloramphenicol inhibition and chlorophyll formation is restored. Concomitantly, chloramphenicol is reduced. Reduction of chloramphenicol in an enzyme extract from Euglena requires NADPH and ferredoxin for maximal activity. Methyl viologen replaces ferredoxin, and when chemically reduced, ferredoxin or methyl viologen reduces chloramphenicol directly. This suggests that the enzyme involved is ferredoxin-NADP reductase. In agreement, crude extracts from wild type and W(3)BUL, a mutant lacking detectable plastids and plastid DNA, when separated on acrylamide gels, show a single band which reduces methyl viologen with NADPH, and its mobility is similar in wild type and in mutant W(3)BUL. The reductase is inducible by light and increases 3-fold in wild type in white or red light and 1.5-fold in W(3)BUL in white light. DCMU does not block chloramphenicol reduction in vivo indicating that electrons originate from sources other than photosynthetic electron transport. We infer that chloramphenicol is reduced by ferredoxin which receives electrons via ferredoxin-NADP reductase. The limiting step is not the enzyme but the source of reducing power which can be supplied from the cytoplasm, probably under control of the blue light receptor. Ferredoxin and ferredoxin NADP reductase appear to be coded in the nuclear genome, synthesized on cytoplasmic ribosomes, and join a group of enzymes which cannot be precisely localized, since they may be active anywhere from their site of synthesis in the cytoplasm to their place of deposition in the chloroplast.

Journal Article↗

PubMed1978

Activation of Chloroplast NADP-linked Glyceraldehyde-3-Phosphate Dehydrogenase by the Ferredoxin/Thioredoxin System.

NADP-glyceraldehyde-3-P dehydrogenase of spinach (Spinacia oleracea) chloroplasts was activated by thioredoxin that was reduced either photochemically with ferredoxin and ferredoxin-thioredoxin reductase or chemically with dithiothreitol. The activation process that was observed with the soluble protein fraction from chloroplasts and with the purified regulatory form of the enzyme was slow relative to the rate of catalysis. The NAD-linked glyceraldehyde-3-P dehydrogenase activity that is also present in chloroplasts and in the purified enzyme preparation was not affected by reduced thioredoxin.When activated by dithiothreitol-reduced thioredoxin, the regulatory form of NADP-glyceraldehyde-3-P dehydrogenase was partly deactivated by oxidized glutathione. The enzyme activated by photochemically reduced thioredoxin was not appreciably affected by oxidized glutathione. The results suggest that although it resembles other regulatory enzymes in its requirements for light-dependent activation by the ferredoxin/thioredoxin system, NADP-glyceraldehyde-3-P dehydrogenase differs in its mode of deactivation and in its capacity for activation by enzyme effectors independently of thioredoxin.

Journal Article↗

PubMed1981

Characterization and Partial Purification of Aldose-6-phosphate Reductase (Alditol-6-Phosphate:NADP 1-Oxidoreductase) from Apple Leaves.

Aldose-6-phosphate reductase (alditol 6-phosphate:NADP 1-oxidoreductase) was isolated and characterized from mature apple leaves (Malus domestica cv. Starkrimson). The enzyme was purified 79-fold. The enzyme catalyzed the following reversible reaction: d-glucose 6-phosphate + NADPH + H(+) right arrow over left arrow d-sorbitol 6-phosphate + NADP(+). No activity was detected when NAD(+) was substituted for NADP(+) or when NADH was substituted for NADPH. The enzyme reduced d-galactose 6-phosphate at a higher rate than d-glucose 6-phosphate. d-Mannose 6-phosphate and 2-deoxy-d-glucose 6-phosphate were reduced at low rates. d-Glucose 1-phosphate, d-fructose 6-phosphate, d-ribose 5-phosphate, d-glucose, and sorbitol did not serve as substrates. The pH optimum for both d-sorbitol 6-phosphate oxidation and d-glucose 6-phosphate reduction was 9.5. The K(m) values for d-sorbitol 6-phosphate oxidation and d-glucose 6-phosphate reduction were 3.9 and 20 millimolar, respectively. AgNO(3) (0.1 millimolar) and p-chloromercuribenzoate (1.0 millimolar) completely inhibited the enzyme.Aldose-6-phosphate reductase activity was also detected in mature leaves from Golden Delicious and Antonovka apples (Malus domestica), Conference and Bartlett pears (Pyrus communis), Redhaven peach (Prunus persica), and Perfection apricot (Prunus armeniaca). This suggests that the enzyme has a wide distribution and plays an important role in sorbitol synthesis.

Journal Article↗

PubMed1981

Enzyme Regulation in C(4) Photosynthesis : PURIFICATION AND PROPERTIES OF THIOREDOXIN-LINKED NADP-MALATE DEHYDROGENASE FROM CORN LEAVES.

NADP-malate dehydrogenase, a light-modulated enzyme of C(4) photosynthesis, was purified to homogeneity from leaves of corn. The pure enzyme was activated by thioredoxin m that was reduced either photochemically (with ferredoxin and ferredoxin-thioredoxin reductase) or chemically (with dithiothreitol). Unactivated corn leaf NADP-malate dehydrogenase had a molecular weight of 50,000 to 60,000 and was chromophorefree. The enzyme appeared to have a high content of serine and glycine and to contain both S-S and SH groups. Consequently, NADP-malate dehydrogenase seems to be capable of undergoing reversible oxidation/reduction during its photoregulation.

Journal Article↗