scholarly journals Unidirectional inhibition and activation of ‘malic’ enzyme of Solanum tuberosum by meso-tartrate

1975 ◽  
Vol 149 (2) ◽  
pp. 349-355 ◽  
Author(s):  
K H Do Nascimento ◽  
D D Davies ◽  
K D Patil
Keyword(s):  
Solanum Tuberosum ◽  
Organic Acids ◽  
Malic Acid ◽  
Active Site ◽  
Malic Enzyme ◽  
Control Site ◽  
Oxidative Decarboxylation ◽  
Reductive Carboxylation ◽  
Similar Explanation ◽  
Stimulation Of

A kinetic study of ‘malic’ enzyme (EC 1.1.1.40) from potato suggests that the mechanism is Ordered Bi Ter with NADP+ binding before malate, and NADPH binding before pyruvate and HCO3-. The analysis is complicated by the non-linearity that occurs in some of the plots. meso-Tartrate is shown to inhibit the oxidative decarboxylation of malate but to activate the reductive carboxylation of pyruvate. To explain these unidirectional effects it is suggested that the control site of ‘malic’ enzyme binds organic acids (including meso-tartrate) which activate the enzyme. meso-Tartrate, however, competes with malate for the active site and thus inhibits the oxidative decarboxylation of malate. Because meso-tartrate does not compete effectively with pyruvate for enzyme-NADPH, its binding at the control site leads to a stimulation of the carboxylation of pyruvate. A similar explanation is advanced for the observation that malic acid stimulates its own synthesis.

scholarly journals Regulation of ‘malic’ enzyme of Solanum tuberosum by metabolites

1974 ◽  
Vol 137 (1) ◽  
pp. 45-53 ◽  
Author(s):  
D. D. Davies ◽  
K. D. Patil
Keyword(s):  
Solanum Tuberosum ◽  
Malic Enzyme ◽  
Energy Charge ◽  
Dicarboxylic Acids ◽  
Oxidative Decarboxylation ◽  
Bivalent Cation ◽  
Ph Values ◽  
Rate Versus ◽  
Reductive Carboxylation

A purification of ‘malic’ enzyme from potato is described. The purified enzyme is specific for NADP and requires a bivalent cation for activity. At pH values below 7 the plot of rate versus malate concentration approximates to normal Michaelis–Menten kinetics. At pH values above 7 the plot of rate versus malate concentration is sigmoid. A number of dicarboxylic acids activate the enzyme and remove the sigmoidicity. The enzyme is inhibited by phosphate, triose phosphates and AMP. In general, effectors of the oxidative decarboxylation of malate behave in the same manner in the reductive carboxylation of pyruvate. The response of the enzyme to energy charge is reported and the physiological significance of the response to metabolites is discussed in relation to the proposed role of the enzyme in the control of pH.

scholarly journals Characterization of an archaeal malic enzyme from the hyperthermophilic archaeonThermococcus kodakaraensisKOD1

Archaea ◽  
2005 ◽  
Vol 1 (5) ◽  
pp. 293-301 ◽  
Author(s):  
Wakao Fukuda ◽  
Yulia Sari Ismail ◽  
Toshiaki Fukui ◽  
Haruyuki Atomi ◽  
Tadayuki Imanaka
Keyword(s):  
Enzyme Activity ◽  
Malic Enzyme ◽  
Hyperthermophilic Archaea ◽  
Oxidative Decarboxylation ◽  
Limited Information ◽  
Gene Encoding ◽  
Malic Enzyme Activity ◽  
Reductive Carboxylation ◽  
Reaction Direction

Although the interconversion between C4 and C3 compounds has an important role in overall metabolism, limited information is available on the properties and regulation of enzymes acting on these metabolites in hyperthermophilic archaea. Malic enzyme is one of the enzymes involved in this interconversion, catalyzing the oxidative decarboxylation of malate to pyruvate as well as the reductive carboxylation coupled with NAD(P)H. This study focused on the enzymatic properties and expression profile of an uncharacterized homolog of malic enzyme identified in the genome of a heterotrophic, hyperthermophilic archaeonT hermococcus kodakaraensisKOD1 (Tk-Mae). The amino acid sequence ofTk-Mae was 52–58% identical to those of malic enzymes from bacteria, whereas the similarities to the eukaryotic homologs were lower. Several catalytically important regions and residues were conserved in the primary structure ofTk-Mae. The recombinant protein, which formed a homodimer, exhibited thermostable malic enzyme activity with strict divalent cation dependency. The enzyme preferred NADP+rather than NAD+, but did not catalyze the decarboxylation of oxaloacetate, unlike the usual NADP-dependent malic enzymes. The apparent Michaelis constant (Km) ofTk-Mae for malate (16.9 mM) was much larger than those of known enzymes, leading to no strong preference for the reaction direction. Transcription of the gene encodingTk-Mae and intracellular malic enzyme activity inT. kodakaraensiswere constitutively weak, regardless of the growth substrates. Possible roles ofTk-Mae are discussed based on these results and the metabolic pathways ofT. kodakaraensisdeduced from the genome sequence.

REGULATION OF THE "MALIC" ENZYME IN NEUROSPORA CRASSA

1967 ◽  
Vol 13 (9) ◽  
pp. 1211-1221 ◽  
Author(s):  
M. W. Zink
Keyword(s):  
Cell Growth ◽  
Neurospora Crassa ◽  
Growth Phase ◽  
Pyruvic Acid ◽  
Malic Acid ◽  
Malic Enzyme ◽  
Enzyme Preparation ◽  
Growth Cycle ◽  
Oxidative Decarboxylation ◽  
Enzyme Repression

"Malic" enzyme has been isolated from Neurospora crassa which can bring about the reversible carboxylation of pyruvic acid. The enzyme is specific to L-malate and NADP and is activated by Mn++ and Mg++. The partially purified enzyme does not decarboxylate oxaloacetate but is competitively inhibited by it. This enzyme is synthesized only during the early stages of the growth cycle and is repressed by acetate. In addition, the oxidative decarboxylation of malic acid is competitively inhibited by aspartic acid; the degree of inhibition depends upon the cell growth phase from which the enzyme is extracted. "Malic" enzyme isolated from a 12-h culture is not significantly inhibited by aspartate. However, this inhibition increases to 90% if an enzyme preparation from a 24-h culture is used. The significance of enzyme repression by acetate and the inhibition of the activity by aspartate are discussed.

The crystal structure of the malic enzyme fromCandidatusPhytoplasma reveals the minimal structural determinants for a malic enzyme

2018 ◽  
Vol 74 (4) ◽  
pp. 332-340 ◽  
Author(s):  
C. E. Alvarez ◽  
F. Trajtenberg ◽  
N. Larrieux ◽  
M. Saigo ◽  
A. Golic ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Active Site ◽  
Malic Enzyme ◽  
Phylogenetic Analyses ◽  
Large Subunit ◽  
Structure Design ◽  
Oxidative Decarboxylation ◽  
Functional Domain ◽  
High Concentration ◽  
Starting Point

Phytoplasmas are wall-less phytopathogenic bacteria that produce devastating effects in a wide variety of plants. Reductive evolution has shaped their genome, with the loss of many genes, limiting their metabolic capacities. Owing to the high concentration of C4compounds in plants, and the presence of malic enzyme (ME) in all phytoplasma genomes so far sequenced, the oxidative decarboxylation of L-malate might represent an adaptation to generate energy. Aster yellows witches'-broom (CandidatusPhytoplasma) ME (AYWB-ME) is one of the smallest of all characterized MEs, yet retains full enzymatic activity. Here, the crystal structure of AYWB-ME is reported, revealing a unique fold that differs from those of `canonical' MEs. AYWB-ME is organized as a dimeric species formed by intertwining of the N-terminal domains of the protomers. As a consequence of such structural differences, key catalytic residues such as Tyr36 are positioned in the active site of each protomer but are provided by the other protomer of the dimer. A Tyr36Ala mutation abolishes the catalytic activity, indicating the key importance of this residue in the catalytic process but not in the dimeric assembly. Phylogenetic analyses suggest that larger MEs (large-subunit or chimeric MEs) might have evolved from this type of smaller scaffold by gaining small sequence cassettes or an entire functional domain. TheCandidatusPhytoplasma AYWB-ME structure showcases a novel minimal structure design comprising a fully functional active site, making this enzyme an attractive starting point for rational genetic design.

Mechanism of regulation of the malic enzyme from Fusarium

1974 ◽  
Vol 20 (4) ◽  
pp. 443-454 ◽  
Author(s):  
M. W. Zink
Keyword(s):  
Malic Acid ◽  
Malic Enzyme ◽  
Kinetic Studies ◽  
Oxidative Decarboxylation ◽  
Mercaptosuccinic Acid ◽  
Substrate Activation ◽  
Phosphate Inhibition ◽  
Phosphoglyceric Acid ◽  
Variable Substrate ◽  
Text Component

The NADP-specific malic enzyme which catalyzes the oxidative decarboxylation of malic acid has been partially purified from extracts of Fusarium oxysporum and some of its kinetic parameters studied. Reciprocal velocity plots with malate as variable substrate are nonlinear except at high NADP concentration, while with NADP as variable substrate the reciprocal plots are linear. Substrate activation by malic acid describes a biphasic character in reciprocal plots. Kinetic studies indicate that there are two binding sites for malic acid. At saturating levels of NADP, two Km components for malic acid, designated as [Formula: see text] and [Formula: see text] are evident. The separation of the two components may have been accomplished; [Formula: see text] component by mercaptosuccinic acid and [Formula: see text] component by either low pH or by phosphate. Inhibition of the purified malic enzyme is nontotal with fructose 1,6-diphosphate, 6-phosphogluconic acid, and 3-phos-phoglyceric acid. The kinetic relationship between fructose 1,6-diphosphate or 6-phospho-gluconate and malic acid is competitive with respect to the [Formula: see text] component and noncompetitive with [Formula: see text] component. Inhibition by 3-phosphoglyceric acid and oxaloacetate with respect to both components is noncompetitive and competitive, respectively. The significance of negative cooperativity and the effect of the above-mentioned inhibitors is discussed.

scholarly journals Crystal structures of non-oxidative decarboxylases reveal a new mechanism of action with a catalytic dyad and structural twists

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Matthias Zeug ◽  
Nebojsa Markovic ◽  
Cristina V. Iancu ◽  
Joanna Tripp ◽  
Mislav Oreb ◽  
...  
Keyword(s):  
Crystal Structures ◽  
Active Site ◽  
Enzyme Engineering ◽  
Base Catalysis ◽  
Oxidative Decarboxylation ◽  
Transition State Stabilization ◽  
Major Bottleneck ◽  
Hydroxybenzoic Acids ◽  
Potassium Binding ◽  
Β Sheet

AbstractHydroxybenzoic acids, like gallic acid and protocatechuic acid, are highly abundant natural compounds. In biotechnology, they serve as critical precursors for various molecules in heterologous production pathways, but a major bottleneck is these acids’ non-oxidative decarboxylation to hydroxybenzenes. Optimizing this step by pathway and enzyme engineering is tedious, partly because of the complicating cofactor dependencies of the commonly used prFMN-dependent decarboxylases. Here, we report the crystal structures (1.5–1.9 Å) of two homologous fungal decarboxylases, AGDC1 from Arxula adenivorans, and PPP2 from Madurella mycetomatis. Remarkably, both decarboxylases are cofactor independent and are superior to prFMN-dependent decarboxylases when heterologously expressed in Saccharomyces cerevisiae. The organization of their active site, together with mutational studies, suggests a novel decarboxylation mechanism that combines acid–base catalysis and transition state stabilization. Both enzymes are trimers, with a central potassium binding site. In each monomer, potassium introduces a local twist in a β-sheet close to the active site, which primes the critical H86-D40 dyad for catalysis. A conserved pair of tryptophans, W35 and W61, acts like a clamp that destabilizes the substrate by twisting its carboxyl group relative to the phenol moiety. These findings reveal AGDC1 and PPP2 as founding members of a so far overlooked group of cofactor independent decarboxylases and suggest strategies to engineer their unique chemistry for a wide variety of biotechnological applications.

scholarly journals The Connectivity Index: An Effective Metric for Grading Epileptogenicity

2019 ◽  
Author(s):  
Qi Yan ◽  
Nicolas Gaspard ◽  
Hitten P Zaveri ◽  
Hal Blumenfeld ◽  
Lawrence J. Hirsch ◽  
...  
Keyword(s):  
Average Distance ◽  
Single Pulse ◽  
Brain Regions ◽  
Control Site ◽  
Connectivity Index ◽  
Evoked Responses ◽  
Seizure Onset ◽  
Seizure Onset Zone ◽  
Site Of Stimulation ◽  
Stimulation Of

AbstractObjectiveTo investigate the performance of a metric of functional connectivity to classify and grade the excitability of brain regions based on evoked potentials to single pulse electrical stimulation (SPES).MethodsPatients who received 1-Hz frequency stimulation between 2003 and 2014 at Yale at prospectively selected contacts were included. The stimulated contacts were classified as seizure onset zone (SOZ), highly irritative zone (IZp) or control. Response contacts were classified as seizure onset zone (SOZ), active interictal (IZp), quiet or other. The normalized number of responses was defined as the number of contacts with any evoked responses divided by the total number of recorded contacts, and the normalized distance is the ratio of the average distance between the site of stimulation and sites of evoked responses to the average distances between the site of stimulation and all other recording contacts. A new metric we labeled the connectivity index (CI) is defined as the product of the two values.Results57 stimulation-sessions in 22-patients were analyzed. The connectivity index (CI) of the SOZ was higher than control (median CI of 0.74 vs. 0.16, p = 0.0002). The evoked responses after stimulation of SOZ were seen at further distance compared to control (median normalized distance 0.96 vs. 0.62, p = 0.0005). It was 1.8 times more likely to record a response at SOZ than in non-epileptic contacts after stimulation of a control site. Habitual seizures were triggered in 27% of patients and 35 % of SOZ contacts (median stimulation intensity 4 mA) but in none of the control or IZp contacts. Non-SOZ contacts in multifocal or poor surgical outcome cases had a higher CI than non-SOZ contacts in those with localizable onsets (medians CI of 0.5 vs. 0.12, p = 0.04). There was a correlation between the stimulation current intensity and the normalized number of evoked responses (r = + 0.49, p 0.01) but not with distance (r = + 0.1, p 0.64)ConclusionsWe found enhanced connectivity when stimulating the SOZ compared to stimulating control contacts; responses were more distant as well. Habitual auras and seizures provoked by SPES were highly predictive of brain sites involved in seizure generation.

Alternative Substrates for Malic Enzyme:  Oxidative Decarboxylation ofl-Aspartate†

Biochemistry ◽  
2002 ◽  
Vol 41 (40) ◽  
pp. 12200-12203 ◽  
Author(s):  
Dali Liu ◽  
Chi-Ching Hwang ◽  
Paul F. Cook
Keyword(s):  
Malic Enzyme ◽  
Oxidative Decarboxylation ◽  
Alternative Substrates

Tyrosyl Residue at or Near the Active Site of Maize NADP-malic Enzyme

1999 ◽  
Vol 36 (1-2) ◽  
pp. 225-231 ◽  
Author(s):  
S.R. Rao ◽  
B.G. Kamath ◽  
A.S. Bhagwat
Keyword(s):  
Active Site ◽  
Malic Enzyme
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