Studies on free and enzyme-bound nicotinamide adenine dinucleotide free radicals

Journal Article · Wed Feb 27 00:00:00 EST 1980 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00525a041· OSTI ID:5279722

Bielski, B H.J. ^[1]; Chan, P C

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1. Brookhaven National Lab., Upton, NY

The spectral and kinetic properties of the NAD free radical have been studied as a function of temperature and pH. The radical decays by second-order kinetics to an enzymatically inactive dimer (NAD)/sub 2/. At 23.5/sup 0/C and pH 7.3 the corresponding rate constant is k/sub 9/ = (7.72 +- 0.78) x 10/sup 7/ M/sup -1/s/sup -1/ with an activation energy E/sub a/ = 3.4 +- 0.4 kcal/mol. Upon attachment of the NAD radical to an enzyme active site, the radical becomes stabilized. The stabilization effect (ratio of the rate of NAD disappearance in the absence and presence of an enzyme) depends upon the nature of the enzyme and varies from 1.54 x 10/sup 2/ for alcohol dehydrogenase, 2.57 x 10/sup 2/ for malate dehydrogenase, 1.1 x 10/sup 3/ for lactate dehydrogenase, to 1.54 x 10/sup 4/ for glyceraldehyde-3-phosphate dehydrogenase. The observed second-order disappearance of enzyme-stabilized NAD is explained by a mechanism that is dependent upon the dissociation constant of the enzyme-NAD complex. 6 figures

• OSTI ID: 5279722
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 102:5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
NAD
CHEMICAL REACTION KINETICS
RADICALS
ACTIVATION ENERGY
ALCOHOLS
DEHYDROGENASES
DIMERS
DISSOCIATION
ENZYMES
PH VALUE
SPECTRAL RESPONSE
TEMPERATURE DEPENDENCE
COENZYMES
ENERGY
HYDROXY COMPOUNDS
KINETICS
NUCLEOTIDES
ORGANIC COMPOUNDS
OXIDOREDUCTASES
REACTION KINETICS
400301* - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)