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  • 1
    Electronic Resource
    Electronic Resource
    Identification of 2-enolbutyrate as the product of the reaction of maize leaf phosphoenolpyruvate carboxylase with (Z)- and (E)-2-phosphoenolbutyrate: evidence from NMR and kinetic measurements (1988)
    s.l. : American Chemical Society
    Biochemistry 27 (1988), S. 177-183 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00401a027
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of DNA polymerase activity in Petunia protoplasts treated with clastogenic agents (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 90 (1994), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Clastogenic agents, i.e. agents that can induce chromosome or DNA breakage, have been shown to enhance the rale of direct gene transfer to protoplasts. The effect was analysed at the enzymatic level using protoplast homogenates as well as intact protoplasts. For that purpose existing procedures were modified to enable measurement of DNA polymerase in vivo. In the system used, external DNA was able to enter the cells without the addition of membrane-permeabilizing compounds. When comparing total DNA polymerase activity of protoplasts irradiated with X-rays or UV-light with that of untreated cells we did not observe significant differences. Incubation of protoplasts with high doses of bleomycin affected total DNA polymerase activity negatively. but dideoxythymidine triphosphate-sensitive activity was not influenced. We conclude that the DNA strand-breaks induced by low doses of X-rays. UV-light or bleomycin do not increase the total or the repair-DNA polymerase activity and. therefore. that the increase in the transformation rates after DNA strand-breaking is not preceded by enhanced DNA polymerase activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1994.tb08800.x
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  • 3
    Electronic Resource
    Electronic Resource
    CO2-concentrating mechanisms in Egeria densa, a submersed aquatic plant (2002)
    Oxford, UK : Blackwell Science, Ltd
    Physiologia plantarum 115 (2002), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Egeria densa is an aquatic higher plant which has developed different mechanisms to deal with photosynthesis under conditions of low CO2 availability. On the one hand it shows leaf pH-polarity, which has been proposed to be used for bicarbonate utilization. In this way, at high light intensities and low dissolved carbon concentration, this species generates a low pH at the adaxial leaf surface. This acidification shifts the equilibrium HCO3–/CO2 towards CO2, which enters the cell by passive diffusion. By this means, E. densa increases the concentration of CO2 available for photosynthesis inside the cells, when this gas is limiting. On the other hand, under stress conditions resulting from high temperature and high light intensities, it shows a biochemical adaptation with the induction of a C4-like mechanism but without Kranz anatomy. Transfer from low to high temperature and light conditions induces increased levels of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) and NADP-malic enzyme (NADP-ME, EC 1.1.1.40), both key enzymes participating in the Hatch-Slack cycle in plants with C4 metabolism. Moreover, one PEPC isoform, whose synthesis is induced by high temperature and light, is phosphorylated in the light, and changes in kinetic and regulatory properties are correlated with changes in the phosphorylation state of this enzyme. In the present review, we describe these two processes in this submersed angiosperm that appear to help it perform photosynthesis under conditions of extreme temperatures and high light intensities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2002.1150402.x
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  • 4
    Electronic Resource
    Electronic Resource
    Interaction of divalent metal ions with the NADP+-malic enzyme from maize leaves (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 81 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effect of several metal ions on NADP+-malic enzyme (EC 1.1.1.40) purified from Zea mays L. leaves was studied Mg2+, Mn2+, Co2+ and Cd2+ were all active metal cofactors. The malic enzyme from maize has a moderately high intrinsic preference for Mn2+ relative to Mg2+ at pH 7.0 and 8.0 Negative cooperativity detected in the binding of Mg2+ at pH 7.0 and 8.0 and in the binding of Mn2+ at pH 7.0 suggests the existence of at least two binding sites with different affinity. All of the activating metal ions have preference for octahedral coordination geometry and have ionic radii of 0.86–1.09 Å. The ions that act as inhibitors are outside this range and/or are incapable of octahedral coordination. Ba2+, Sr2+, Cd2+, Ca2+, Be2+, Ni2+, Cu2+, Zn2+, Co2+, Hg2+ showed mixed-type inhibition. The reciprocal of their K1 values follow the order of their apparence in the Irving-Williams series of stability that derives in part from size effects. It is suggested that the size of the ions may play a partial role in determining the strength of the metal interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb05085.x
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  • 5
    Electronic Resource
    Electronic Resource
    Oligomeric enzymes in the C4 pathway of photosynthesis (1990)
    Springer
    Photosynthesis research 26 (1990), S. 161-170 
    Details
    ISSN: 1573-5079
    Keywords: NAD-malic enzyme ; NADP-malic enzyme ; NADP-malic dehydrogenase ; pyruvate ; phosphate dikinase ; regulatory protein ; phosphoenolpyruvate carboxylase ; protein structure ; enzyme regulation ; C4 metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This review deals with the factors controlling the aggregation-state of several enzymes involved in C4 photosynthesis, namely phosphoenolpyruvate carboxylase, NAD-and NADP-malic enzyme, NADP-malic dehydrogenase and pyruvate, phosphate dikinase and its regulatory protein. All of these enzymes are oligomeric and have been shown to undergo changes in their quaternary structure in vitro under different conditions. The activity changes linked to variations in aggregation-state are discussed in terms of their putative physiological role in the regulation of C4 metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00033129
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  • 6
    Electronic Resource
    Electronic Resource
    Interaction of analogues of substrate with NADP-malic enzyme from maize leaves (1994)
    Springer
    Photosynthesis research 39 (1994), S. 67-73 
    Details
    ISSN: 1573-5079
    Keywords: Zea mays ; C4-photosynthesis ; decarboxylation ; NADP-ME type ; l-malate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of structural analogues of l-malate was studied on NADP-malic enzyme purified from Zea mays L. leaves. Among the compounds tested, the organic acids behaved as more potent inhibitors at pH 7.0 than at pH 8.0, suggesting that the dimeric form was more susceptible to the inhibition than the tetrameric form of the enzyme. Oxalate, ketomalonate, hydroxymalonate, malonate, oxaloacetate, tartrate, α-hydroxybutyrate, α-ketobutyrate, α-ketoglutarate and α-hydroxyglutarate exhibited linear competitive inhibition with respect to the substrate l-malate at pH 8.0. On the other hand, glyoxylate and glycolate turned out to be non-competitive inhibitors, while glycolaldehyde, succinate, fumarate, maleate and β- and γ-hydroxybutyrate had no effect on the enzyme activity, at the concentrations assayed. These results suggest that the extent of inhibition was dependent on the size of the analogues and that the presence of an 1-carboxyl group along with a 2-hydroxyl or 2-keto group was important for binding of the substrate analogue to the enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00027144
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  • 7
    Electronic Resource
    Electronic Resource
    Kinetic mechanism of NADP-malic enzyme from maize leaves (1995)
    Springer
    Photosynthesis research 43 (1995), S. 1-9 
    Details
    ISSN: 1573-5079
    Keywords: Zea mays ; C4-photosynthesis ; decarboxylation ; NADP-ME type ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The kinetic mechanism of NADP-dependent malic enzyme purified from maize leaves was studied in the physiological direction. Product inhibition and substrate analogues studies with 3′ aminopyridine dinucleotide phosphate and tartrate indicate that the enzyme reaction follows a sequential ordered Bi-Ter kinetic mechanism. NADP is the leading substrate followed by l-malate and the products are released in the order of CO2, pyruvate and NADPH. The enzyme also catalyzes a slow, magnesium-dependent decarboxylation of oxaloacetate and reduction of pyruvate and oxaloacetate in the presence of NADPH to produce l-lactate and l-malate, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029456
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  • 8
    Electronic Resource
    Electronic Resource
    Involvement of thiol groups in the activity of phosphoenolpyruvate carboxylase from maize leaves (1984)
    Springer
    Photosynthesis research 5 (1984), S. 215-226 
    Details
    ISSN: 1573-5079
    Keywords: Cysteine modification ; Maize leaf ; Phosphoenolpyruvate carboxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Purified maize leaf phosphoenolpyruvate carboxylase (EC 4.1.1.31) was completely inactivated by several thiol-modifying reagents, including, CuCl2, CdCl2 and N-ethylmaleimide. The inactivation by CuCl2 could be reversed by dithiothreitol, suggesting the involvement of vicinal dithiols in the inactivation process. Complete inactivation of phosphoenolpyruvate carboxylase was correlated with the incorporation of two mol (3H)N-ethylmaleimide per 100-kilodalton subunit. The total protection of the enzyme against N-ethylmaleimide inactivation afforded by the substrate, phosphoenolpyruvate, was correlated with the protection of one mol (3H)N-ethylmaleimide reactive residue per mol subunit. The complete inactivation of phosphoenolpyruvate carboxylase by N-ethylmaleimide and the protection afforded by phosphoenolpyruvate against modification suggest the presence of an essential cysteine residue in the catalytic site of the C4 leaf enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00030021
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  • 9
    Electronic Resource
    Electronic Resource
    Malate metabolism by NADP-malic enzyme in plant defense (1999)
    Springer
    Photosynthesis research 61 (1999), S. 99-105 
    Details
    ISSN: 1573-5079
    Keywords: C3 ; C4 ; UV-B ; stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Malate is involved in various metabolic pathways, and there are several enzymes that metabolize it. One important malate metabolizing enzyme is NADP-malic enzyme (NADP-ME). NADP-ME functions in many different pathways in plants, having an important role in C4 photosynthesis where it releases the CO2 to be used in carbon fixation by Rubisco. Apart from this specialized role, NADP-ME is thought to fulfill diverse housekeeping functions because of its universal presence in different plant tissues. NADP-ME is induced after wounding or exposure to UV-B radiation. In this way, the enzyme is implicated in defense-related deposition of lignin by providing NADPH for the two NADPH-dependent reductive steps in monolignol biosynthesis. On the other hand, it can supply NADPH for flavonoid biosynthesis as many steps in the flavonoid biosynthesis pathway require reductive power. Pyruvate, another product of NADP-ME reaction, can be used for obtaining ATP through respiration in the mitochondria; and may serve as a precursor for synthesis of phosphoenolpyruvate (PEP). PEP is utilized in the shikimate pathway, leading to the synthesis of aromatic amino acids including phenylalanine, the common substrate for lignin and flavonoid synthesis. Moreover, NADP-ME can be involved in mechanisms producing NADPH for synthesis of activated oxygen species that are produced in order to kill or damage pathogens. In conclusion, an increase in the levels of NADP-ME could provide building blocks and energy for biosynthesis of defense compounds, suggesting a role of malate metabolism in plant defense.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006209003096
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  • 10
    Electronic Resource
    Electronic Resource
    Analogues of NADP+ as inhibitors and coenzymes for NADP+ malic enzyme from maize leaves (1991)
    Springer
    Photosynthesis research 28 (1991), S. 69-76 
    Details
    ISSN: 1573-5079
    Keywords: C4-photosynthesis ; decarboxylation ; NADP+-ME type
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Structural analogues of the NADP+ were studied as potential coenzymes and inhibitors for NADP+ dependent malic enzyme from Zea mays L. leaves. Results showed that 1, N6-etheno-nicotinamide adenine dinucleotide phosphate (∈ NADP+), 3-acetylpyridine-adenine dinucleotide phosphate (APADP+), nicotinamide-hypoxanthine dinucleotide phosphate (NHDP+) and β-nicotinamide adenine dinucleotide 2′: 3′-cyclic monophosphate (2′3′NADPc+) act as alternate coenzymes for the enzyme and that there is little variation in the values of the Michaelis constants and only a threefold variation in Vmax for the five nucleotides. On the other hand, thionicotinamide-adenine dinucleotide phosphate (SNADP+), 3-aminopyridine-adenine dinucleotide phosphate (AADP+), adenosine 2′-monophosphate (2′AMP) and adenosine 2′: 3′-cyclic monophosphate (2′3′AMPc) were competitive inhibitors with respect to NADP+, while β-nicotinamide adenine dinucleotide 3′-phosphate (3′NADP+), NAD+, adenosine 3′-monophosphate (3′AMP), adenosine 2′: 5′-cyclic monophosphate (2′5′AMPc), 5′AMP, 5′ADP, 5′ATP and adenosine act as non-competitive inhibitors. These results, together with results of semiempirical self-consistent field-molecular orbitals calculations, suggest that the 2′-phosphate group is crucial for the nucleotide binding to the enzyme, whereas the charge density on the C4 atom of the pyridine ring is the major factor that governs the coenzyme activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00033716
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