The rate of hydrolysis of phosphomonoester dianions and the exceptional catalytic proficiencies of protein and inositol phosphatases.
To evaluate the proficiency of phosphatases as catalysts, the rate of the uncatalyzed hydrolysis of simple phosphate monoester dianions was estimated by extrapolating rates measured over a range of high temperatures. The rate of spontaneous hydrolysis of phenyl phosphate dianion indicates that a linear free energy relationship reported earlier is reliable for leaving groups whose conjugate acids have pKa values up to at least 10. Using Teflon reaction vessels, it proved possible to follow the hydrolysis of methyl phosphate and 3-(4-carboxy)-2,2-dimethylpropyl phosphate in strong alkali. Even in 1 M KOH, the reaction was found to be specific acid catalyzed. These results establish an upper limit for dianion reactivity, which had been overestimated earlier as a result of the leaching by alkali of silicic acid from quartz reaction vessels. The present findings indicate that the half-time for attack by water on alkyl phosphate dianions is 1.1 x 10(12) years (k = 2 x 10(-20) s) at 25 degrees C and that phosphatases involved in cell signaling and regulation produce the largest rate enhancements that have been identified thus far. Protein phosphatase-1 and inositol 1-phosphatase exceed all other known enzymes in their affinities for the altered substrates in the transition state.
Lad
Chetan
C
Centre for Chemical Biology, Krebs Institute for Biomolecular Science, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom.
Williams
Nicholas H
NH
Wolfenden
Richard
R
D000838:Anions; D002384:Catalysis; D006868:Hydrolysis; D007700:Kinetics; D010755:Organophosphates / Q000737:chemistry / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000737:chemistry* / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D054645:Protein Phosphatase 1; D013379:Substrate Specificity; D013816:Thermodynamics
D000838:Anions; D010755:Organophosphates; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D010744:Phosphoric Monoester Hydrolases; C021822:myo-inositol-1 (or 4)-monophosphatase