Regulatory site of inorganic pyrophosphatase. Nonhyperbolic kinetics of enzymatic reaction at low substrate concentrations
The initial rate of PP/sub 1/ hydrolysis by inorganic pyrophosphatase from baker's yeast was analyzed as a function of the concentrations of the Mg-PP/sub 1/ complex (substrate) and Mg/sup 2 +/ ions (activator) at substrate concentrations down to 0.1 ..mu..M. Lineweaver-Burk plots for the enzyme in equilibrium with Mg/sup 2 +/ ions were nonlinear at fixed Mg/sup 2 +/ concentrations, which cannot be explained within the framework of previously proposed models of the reaction. The nonlinearity is retained for the monomeric form of the enzyme and indicates that the enzyme has a regulatory site capable of tightly binding free PP/sub 1/ (K/sub d/ approx. 0.02 ..mu..M). A new model of the reaction is proposed in which Mg-PP/sub 1/, PP/sub 1/, and Mg/sup 2 +/ are bound to the enzyme in random order and filling of the regulatory site decreases the dissociation constant of the protein-Mg complex from 4.7 to 0.025 mM. It was concluded that PP/sub 1/ and Mg/sup 2 +/ are regulators of pyrophosphatase activity under physiological conditions.
- Research Organization:
- Lomonosov Moscow State Univ., Moscow (Russian Federation)
- OSTI ID:
- 5841969
- Journal Information:
- Biochemistry (Engl. Transl.); (United States), Vol. 51:2; Other Information: Translated from Biokhimiya; 51: No. 2, 179-187(Feb 1986)
- Country of Publication:
- United States
- Language:
- English
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PHOSPHATASES
ENZYME ACTIVITY
PYROPHOSPHATES
BIOCHEMICAL REACTION KINETICS
ENZYMATIC HYDROLYSIS
RADIOENZYMATIC ASSAY
BIOCHEMISTRY
COMPUTERIZED SIMULATION
DISSOCIATION
LABELLED COMPOUNDS
LABELLING
MAGNESIUM COMPLEXES
MAGNESIUM COMPOUNDS
MATHEMATICAL MODELS
NONLINEAR PROBLEMS
PHOSPHORUS 32
QUANTITY RATIO
SUBSTRATES
YEASTS
ALKALINE EARTH METAL COMPLEXES
ALKALINE EARTH METAL COMPOUNDS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DAYS LIVING RADIOISOTOPES
DECOMPOSITION
ENZYMES
ESTERASES
FUNGI
HYDROLASES
HYDROLYSIS
ISOTOPES
KINETICS
LIGHT NUCLEI
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MICROORGANISMS
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ODD-ODD NUCLEI
OXYGEN COMPOUNDS
PHOSPHORUS COMPOUNDS
PHOSPHORUS ISOTOPES
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REACTION KINETICS
SIMULATION
SOLVOLYSIS
550201* - Biochemistry- Tracer Techniques