PMID: 2558726Dec 12, 1989

The substrate proton of the pyruvate kinase reaction

Biochemistry
I A Rose, D J Kuo

Abstract

The pyruvate kinase reaction occurs in separate phosphate- and proton-transfer stages: (formula; see text) K+, Mg2+, and Mg.ADP are known to be required for the phosphoryl transfer step, and K+ and Mg2+ with allosteric stimulation by MgATP are important for proton transfer. This paper uses the isotope trapping method with 3H-labeled water to identify the proton donor and determine when in the sequence of the catalytic cycle it is generated. When the enzyme was allowed to exchange briefly with 3H2O (pulse phase) and then diluted into a mixture containing PEP, ADP, and the cofactor K+, Mg2+, or Co2+ in D2O (chase phase), an amount of [3H]pyruvate was formed in great excess of the amount expected from steady-state catalysis in the diluted 3H-labeled water. With K+, Mg2+, and ADP at pH 6-9.5 in the pulse phase, a limit of 1.25 enzyme equiv of 3H were trapped. The concentration of PEP required for half-maximum trapping was 14-fold greater than its steady-state Km. Therefore, the rate constant for dissociation of the donor proton is estimated to be 14 times the steady-state rate of [3H]pyruvate formation, approximately 109 s-1, or 1500 s-1. At pD 6.4, Mg2+ and ADP were required in the chase, indicating that the ADP in the pulse was n...Continue Reading

References

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Citations

Jun 7, 1976·Biochimica Et Biophysica Acta·S R Ford, J L Robinson
Jan 1, 1978·The Biochemical Journal·L G Dann, H G Britton
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Dec 1, 1958·Archives of Biochemistry and Biophysics·A TIETZ, S OCHOA

Related Concepts

Complex (molecular entity)
Potassium
Pyruvate Measurement
Adenosine Triphosphate, Magnesium Salt
Pyruvate Kinase
Phosphate Measurement
Protons
Pyruvate
Substrate Specificity
Pyruvate Kinase Measurement

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