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Spectro photo fluorometric evidence of negatively cooperative binding of warfarin and phenyl butazone to human serum albumin


, : Spectro photo fluorometric evidence of negatively cooperative binding of warfarin and phenyl butazone to human serum albumin. Life Sciences 26(3): 173-180

Competition between drugs for common binding sites on plasma proteins is an often discussed mechanism of drug interaction. The validity of the concept that phenylbutazone displaces warfarin from human serum albumin (HSA) by direct competition for the same sites was investigated. The fluorescence enhancement titration procedure of Kolb and Weber was used to characterize the warfarin-HSA interaction under the following conditions: excitation and emission wavelengths - 310 and 390 nm, respectively; buffer 0.1 M phosphate, pH 7.0 (25.degree. C) and (HSA) = 10-6M. The titrations were then repeated in the presence of varying concentrations of phenylbutazone (10-6 to 5 .times. 10-4 M). Bjerrum plots of the data showed a shift of the warfarin-HSA binding curves to higher free levels of warfarin with increasing concentrations of phenylbutazone. This shift was saturable, contrary to expectation for directly competitive antagonism. Together with indirect evidence from the literature, the results suggest that displacement of warfarin by phenylbutazone is via a negatively cooperative mechanism rather than by direct competition.


Accession: 006460094

PMID: 7360001

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Related references

Madsen B.W.; Ellis G.M., 1981: Cooperative interaction of warfarin and phenyl butazone with human serum albumin. Whether phenylbutazone displaces warfarin from human serum albumin (HSA) by direct competition was studied using standard equilibrium dialysis. A number of titration curves for [14C]warfarin (4-1000 .mu.M) in the presence of fixed concentrations o...

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