scholarly journals Properties and regulation of leaf nicotinamide–adenine dinucleotide phosphate–malate dehydrogenase and ‘malic’ enzyme in plants with the C4-dicarboxylic acid pathway of photosynthesis

1970 ◽  
Vol 119 (2) ◽  
pp. 273-280 ◽  
Author(s):  
Hilary S. Johnson ◽  
M. D. Hatch
Keyword(s):  
Dicarboxylic Acid ◽  
Malate Dehydrogenase ◽  
Malic Enzyme ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Maximum Velocity ◽  
Enzyme Reaction ◽  
Reverse Direction ◽  
Leaf Extracts ◽  
Ph Optimum ◽  
Acid Pathway

1. NADP–malate dehydrogenase and `malic' enzyme in maize leaf extracts were separated from NAD–malate dehydrogenase and their properties were examined. 2. The NADP–malate dehydrogenase was nicotinamide nucleotide-specific but otherwise catalysed a reaction comparable with that with the NAD-specific enzyme. By contrast with the latter enzyme, a thiol was absolutely essential for maintaining the activity of the NADP–malate dehydrogenase, and the initial velocity in the direction of malate formation, relative to the reverse direction, was faster. 3. For the `malic' enzyme reaction the Km for malate was dependent on pH and the pH optimum varied with the malate concentration. At their respective optimum concentrations the maximum velocity for this enzyme was higher with Mg2+ than with Mn2+. 4. The NADP–malate dehydrogenase in green leaves was rapidly inactivated in the dark and was reactivated when plants were illuminated. Reactivation of the enzyme extracted from darkened leaves was achieved simply by adding a thiol compound. 5. The activity of both enzymes was low in etiolated leaves of maize plants grown in the dark but increased 10–20-fold, together with chlorophyll, when leaves were illuminated. 6. The activity of these enzymes in different species with the C4-dicarboxylic acid pathway was compared and their possible role in photosynthesis was considered.

scholarly journals Nicotinamide-adenine dinucleotide-linked “malic” enzyme in flight muscle of the tse-tse fly (Glossina) and other insects

1976 ◽  
Vol 160 (2) ◽  
pp. 253-262 ◽  
Author(s):  
J B Hoek ◽  
D J Pearson ◽  
N K Olembo
Keyword(s):  
Malate Dehydrogenase ◽  
Malic Enzyme ◽  
Flight Muscle ◽  
Intracellular Localization ◽  
Deae Cellulose ◽  
Partial Purification ◽  
Decarboxylase Activity ◽  
Matrix Space ◽  
Oxaloacetate Decarboxylase ◽  
Ph Optimum

1. A high activity of NAD-linked ‘malic’ enzyme was found in homogenates of flight muscle of different species of tse-tse fly (Glossina). The activity was the same as, or higher than, that of malate dehydrogenase and more than 20-fold that of NADP-linked ‘malic’ enzyme. A similar enzyme was found in the flight muscle of all other insects investigated, but at much lower activities. 2. ACa2+-stimulated oxaloacetate decarboxylase activity was present in all insect flight-muscle preparations investigated, in constant proportion to the NAD-linked ‘malic’ enzyme. 3. A partial purification of the NAD-linked ‘malic’ enzyme from Glossina was effected by DEAE-cellulose chromatography, which separated the enzyme from malate dehydrogenase and NADP-linked ‘malic’ enzyme, but not from oxaloacetate decarboxylase. 4. The intracellular localization of the NAD-linked ‘malic’ enzyme was predominantly mitochondrial; latency studies suggested a localization in the mitochondrial matrix space. 5. Studies on the partially purified enzyme demonstrated that it had a pH optimum between 7.6 and 7.9. It required Mg2+ or Mn2+ for activity; Ca2+ was not effective. The maximum rate was the same with either cation, but the concentration of Mn2+ required was 100 times less than that of Mg2+. Acitivity with NADP was only 1-3% of that with NAD, unless very high (greater than 10mM) concentrations of Mn2+ were present. 6. It is suggested that the NAD-linked ‘malic’ enzyme functions in the proline-oxidation pathway predominant in tse-tse fly flight muscle.

Inhibition of phosphoenolpyruvate carboxylase from C4 plants by malate and aspartate

1975 ◽  
Vol 53 (17) ◽  
pp. 1925-1933 ◽  
Author(s):  
S. C. Huber ◽  
G. E. Edwards
Keyword(s):  
Phosphoenolpyruvate Carboxylase ◽  
Maximum Velocity ◽  
C4 Plants ◽  
Digitaria Sanguinalis ◽  
Leaf Extracts ◽  
Ph Optimum ◽  
Pep Carboxylase ◽  
Assay Mixture ◽  
Acid Inhibitor ◽  
Rate Limiting

The activity of phosphoenolpyruvate carboxylase in leaf extracts of C4 plants has been shown to be inhibited by the C4 acids malate and aspartate. The magnitude of inhibition observed with phosphoenolpyruvate carboxylase from Digitaria sanguinalis leaves was dependent on the pH of the assay mixture and the concentration of phosphoenolpyruvate (PEP), Mg2+. and the C4 acid inhibitor. The percentage inhibition decreased with increasing pH up to 8.5. At rate-limiting concentrations of phosphoenolpyruvate the pH optimum of the enzyme was 7.8, whereas the enzyme partially inhibited by malate or aspartate had a pH optimum of roughly 8.3. Malate and aspartate inhibited the enzyme by increasing the apparent Km for phosphoenolpyruvate without altering the maximum velocity, such that inhibition was greatest at rate-limiting concentrations of PEP but was not observed at saturating (3 mM) substrate levels. Glucose-6-P. an activator of PEP carboxylase, decreased the apparent Km for PEP and reversed the inhibition by malate and aspartate. Inhibition was also dependent on the concentration of Mg2+. At 1 mM Mg2+, 1 mM malate caused 60% inhibition, but at 5 mM Mg2+ the inhibition was reduced to 15%. Mg2+ at concentrations from 1 to 5 mM had no effect on the apparent Km for PEP. With Sephadex extracts of PEP carboxylase from leaves of D. sanguinalis, malate and aspartate were equally inhibitory, with roughly 2 mM levels required for 50% inhibition. Both malate and aspartate were inhibitory with PEP carboxylase extracted from leaves of a variety of C4∙ but not C3∙ plants. The significance of the observed inhibition and activation of PEP carboxylase by metabolites is discussed in relation to C4 photosynthesis.

scholarly journals A new enzyme for the interconversion of pyruvate and phosphopyruvate and its role in the C4 dicarboxylic acid pathway of photosynthesis

1968 ◽  
Vol 106 (1) ◽  
pp. 141-146 ◽  
Author(s):  
M. D. Hatch ◽  
C. R. Slack
Keyword(s):  
Zea Mays ◽  
Dicarboxylic Acid ◽  
Sugar Cane ◽  
Sorghum Vulgare ◽  
Leaf Extracts ◽  
Tropical Grasses ◽  
Thiol Compound ◽  
Acid Pathway

1. An enzyme was isolated from leaves of tropical grasses that catalyses the reversible conversion of pyruvate, ATP and orthophosphate into phosphopyruvate, AMP and pyrophosphate. A requirement for Mg2+ could not be replaced by Mn2+ or Ca2+. 2. By replacing orthophosphate with [32P]orthophosphate or with arsenate, evidence was provided that the orthophosphate consumed appears in pyrophosphate. 3. Without Mg2+ or 2-mercaptoethanol the enzyme was rapidly and irreversibly inactivated. EDTA only partially replaced the requirement for the thiol compound. The enzyme was considerably more unstable at 0° or when frozen than at 22°. Even with the best conditions devised the enzyme lost about 25% of its activity every 3hr. 4. The activities of the enzyme in leaves of the tropical grasses sugar cane (Saccharum hybrid var. Pindar), maize (Zea mays) and sorghum (Sorghum vulgare) were comparable with their maximum photosynthesis rates. The enzyme was not detectable in leaf extracts from several other plants. 5. Its role in photosynthesis is discussed.

Multiple isotope effects with alternative dinucleotide substrates as a probe of the malic enzyme reaction

Biochemistry ◽  
1991 ◽  
Vol 30 (23) ◽  
pp. 5755-5763 ◽  
Author(s):  
Paul M. Weiss ◽  
Sandhya R. Gavva ◽  
Ben G. Harris ◽  
Jeffrey L. Urbauer ◽  
W. W. Cleland ◽  
...  
Keyword(s):  
Malic Enzyme ◽  
Isotope Effects ◽  
Enzyme Reaction
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