Study of isotope effects on protein binding by gas chromatography/mass spectrometry of theophylline–phenobarbitone and 2H, 13C, 15N isotopomers

✍ Scribed by Y. Cherrah; J. B. Falconnet; M. Desage; J. L. Brazier; R. Zini; J. P. Tillement

• Publisher: John Wiley and Sons
• Year: 1988
• Tongue: English
• Weight: 452 KB
• Volume: 17
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/bms.1200170403

✦ Synopsis

We describe a comparative study of human serum albumin (HSA) binding by equilibrium dialysis (pH 7.4, 37 "C, 3 h) for two groups of isotopic analogues: theophylline and 1-C(*H,)theophylliae; unlabelled, 5(ethyl('H,)), -5(phenyl('H,)) and 1,3-1SN;213C-pbenobarbitone. Bound and free drug fractions are quantified by combined gas chromatography/mass spectrometry. In three instances, protein binding parameters are greatly affected by isotopic substitution, namely for: theophylline and l-C('H,)theophylline with isotope effects on total binding site concentration (N), affinity constant (KJ and extent of HSA binding (%) respectively, equal to: NJN, = 0.51; KaL/K8n = 1.78; %L/%H = 0.96 (L (light) and H (heavy) represent the unlabelled and labelled analogue respectively); pbenobarbitone/-5-(phenyl('Hs))phenobarbitone, NL/N, = 1.72; KaL/K8,, = 0.56; %L/%H = 1.26; pheno-barbit0ne/l,3-'~N;%~~C phenobarbitone, NL/NH = 2.95; K8L/KaH = 0.44; %L/%H = 1.32, together with a change from one (saturable) to two (saturable + non-saturable) families of albumin binding sites in the latter case.

Contrasting with these data, no HSA binding isotope effect was observed on phenobarbitone C5 ethyl deuteration.