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

Journal Article · Wed Feb 27 04:00:00 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

---

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), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 102:5; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

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