Metal ion effects on enolase activity
Most metal binding studies with yeast enolase suggest that two metals per monomer are required for catalytic activity. The functions of metal I and metal II have not been unequivocally defined. In a series of kinetic experiments where the concentration of MgII is kept constant at subsaturating levels (1mM), the addition of MnII or of ZnII gives a hyperbolic decrease in activity. The final velocity of these mixed metal systems is the same velocity obtained with either only MnII or ZnII respectively. The concentration of MnII (40 ..mu..M) or of Zn (2..mu..M) which gives half maximal effect in the presence of (1mM) MgII is approximately the same as the Km' value for MnII (9..mu..M) or ZnII (3..mu..M) respectively. Direct binding of MnII to enolase in the absence and presence of MgII shows that MnII and MgII compete for the same metal site on enolase. In the presence of 2-phosphoglycerate (2-PGA) and MgII, only a single site is occupied by MnII. Results suggest MnII at site I and MgII at site II. PRR and high resolution /sup 1/H and /sup 31/P NMR studies of enzyme-ligand complexes containing MnII and MgII and MnII are consistent with this model. /sub 31/P measurements allow a measure of the equilibrium constant (0.36) for enolase. Saturation transfer measurements yield net rate constants (k/sub f/ = 0.49s/sup -1/; k/sub r/ = 1.3s/sup -1/) for the overall reaction. These values are smaller than k/sub cat/ (38s/sup -1/) measured under analogous conditions. The cation at site I appears to determine catalytic activity.
- Research Organization:
- Univ. of Notre Dame, IN
- OSTI ID:
- 5325222
- Report Number(s):
- CONF-8606151-
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Vol. 45:6; Conference: 76. annual meeting of the Federation of American Society for Experimental Biology, Washington, DC, USA, 8 Jun 1986
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
62 RADIOLOGY AND NUCLEAR MEDICINE
CARBON-OXYGEN LYASES
ENZYME ACTIVITY
MAGNESIUM
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL EFFECTS
MANGANESE
ZINC
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
PHOSPHORUS 31
YEASTS
ALKALINE EARTH METALS
ELEMENTS
ENZYMES
FUNGI
ISOTOPES
KINETICS
LIGHT NUCLEI
LYASES
MAGNETIC RESONANCE
METALS
MICROORGANISMS
NUCLEI
ODD-EVEN NUCLEI
PHOSPHORUS ISOTOPES
PLANTS
REACTION KINETICS
RESONANCE
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENTS
560302* - Chemicals Metabolism & Toxicology- Microorganisms- (-1987)
550201 - Biochemistry- Tracer Techniques
550600 - Medicine