Alternate substrates and isotope effects as a probe of the malic enzyme reaction
Dissociation constants for alternative dinucleotide substrates and competitive inhibitors suggest that the dinucleotide binding site of the Ascaris suum NAD-malic enzyme is hydrophobic in the vicinity of the nicotinamide ring. Changes in the divalent metal ion activator from Mg{sup 2+} to Mn{sup 2+} or Cd{sup 2+} results in a decrease in the dinucleotide affinity and an increase in the affinity for malate. Primary deuterium and {sup 13}C isotope effects obtained with the different metal ions suggest either a change in the transition state structure for the hydride transfer or decarboxylation steps or both. Deuterium isotope effects are finite whether reactants are maintained at saturating or limiting concentrations with all the metal ions and dinucleotide substrates used. For the native enzyme, primary deuterium isotope effects increase with a concomitant decrease in the {sup 13}C effects when NAD is replaced by an alternate dinucleotide substrate different in redox potential.
- Research Organization:
- University of North Texas, Denton, TX (USA)
- OSTI ID:
- 5222888
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
560300* -- Chemicals Metabolism & Toxicology
59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AFFINITY
ALKALINE EARTH METAL COMPOUNDS
ASCARIDAE
ASCARIS
ASCHELMINTHES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL EFFECTS
CADMIUM COMPOUNDS
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
COENZYMES
DEUTERIUM
ENZYMES
EVEN-ODD NUCLEI
HELMINTHS
HYDROGEN ISOTOPES
HYDROXY ACIDS
ISOTOPE APPLICATIONS
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
MAGNESIUM COMPOUNDS
MALIC ACID
MANGANESE COMPOUNDS
MEMBRANE PROTEINS
METABOLISM
MOLECULAR STRUCTURE
NAD
NEMATODES
NUCLEI
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
PARASITES
PROTEINS
REACTION KINETICS
RECEPTORS
STABLE ISOTOPES
SUBSTRATES
TRACER TECHNIQUES
TRANSITION ELEMENT COMPOUNDS