Electrostatic control of the rate-determining step of the copper, zinc superoxide dismutase catalytic reaction
The dependence of the activity of bovine Cu,Zn superoxide dismutase on pH and ionic strength was extensively investigated in the ranges of pH 7.4-pH 12.3 and of ionic strength of 0.02-0.25 M. The results obtained indicate that two positively charged groups having pK values of approximately 10.1 and 10.8 are involved in the control of the activity. On the basis of previous work on the three-dimensional structure and on the chemically modified enzyme, these groups are likely to be lysine side chains, in particular Lys-120 and Lys-134. The oxidation state of the enzyme-bound copper ion at the steady state was found to be the same at either pH 7.4 or pH 11.5. The diffusion of superoxide ion into the active site, which is controlled by the positive charges around the active site itself, appears to be the rate-determining step of the dismutation reaction. NMR measurements of the relaxation rates of F/sup -/ showed that this control also applies to the access of F/sup -/ to the active site. Comparison of the nuclear relaxation rates of F/sup -/ with the enzyme activity indicates that F/sup -/ relaxation is controlled by the deprotonation of the group with pK approx. 10.8, which appears to be responsible for about 50% of the total activity measured at neutral pH.
- Research Organization:
- Univ. of Venice, Italy
- OSTI ID:
- 6180492
- Journal Information:
- Biochemistry; (United States), Vol. 26:11
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPEROXIDE DISMUTASE
BIOCHEMICAL REACTION KINETICS
NUCLEAR MAGNETIC RESONANCE
CATALYSIS
CATIONS
CATTLE
COPPER COMPOUNDS
FLUORINE 19
PH VALUE
ZINC COMPOUNDS
ANIMALS
CHARGED PARTICLES
DOMESTIC ANIMALS
ENZYMES
FLUORINE ISOTOPES
IONS
ISOTOPES
KINETICS
LIGHT NUCLEI
MAGNETIC RESONANCE
MAMMALS
NUCLEI
ODD-EVEN NUCLEI
OXIDOREDUCTASES
REACTION KINETICS
RESONANCE
RUMINANTS
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques