Human serum albumin is known to have two major and selective drug binding sites, termed sites I and II. The fluorescent probes, dansylamide and dansylsarcosine selectively interact with sites I and II, respectively. However, the binding site of the fluorescent probe dansylglycine on human serum albumin is not clear from the literature. This study investigated whether dansylglycine interacts tightly with site I or II. Spectrofluorimetric titrations (quenching and complex) and circular dichroism measurements were performed to determine the binding characteristics of dansylglycine to human serum albumin. Modification in probe fluorescence was described by fluorescence titrations to be a result of competitive displacement by ligands. The pattern of displacement of this probe by several ligands whose primary binding sites are exactly known, enabled the identification of its specific binding site. The fluorescence of dansylglycine is only extensively changed when ligands of site II are added, suggesting that it strongly interacts with the benzodiazepine/indole binding site on human serum albumin.

Stereoselective binding of nonsteroidal anti-inflammatory drugs (NSAIDs) can be studied using various techniques. Thus the results obtained by different investigators may be poorly consistent and even contradictory. NSAIDs are bound stereoselectively to serum albumin to different degrees depending on the drug investigated (ibuprofen, indoprofen, carprofen, etodolac, ketoprofen and flurbiprofen). For other drugs, both enantiomers are bound to a similar extent (pirprofen, fenoprofen). This stereoselectivity could vary with experimental conditions, in particular with protein concentration (ketoprofen, etodolac), leading to individual differences. Finally, the stereoselectivity of protein binding and of pharmacokinetics can be compared: differences in binding between enantiomers can explain their differences in pharmacokinetics, once metabolic properties such as inversion have been taken into account.

Most NSAIDs are chiral molecules: they exist under 2 configurations of non-superimposable mirror images which are termed enantiomers or optical isomers or optical antipodes. Direct or indirect (resolution) methods are used to separate this equal mixture of compounds. Some of the enantiomers of the NSAIDs are able to undergo chiral inversion from the inactive R(-) to the active S(+) form. The pharmacokinetics in terms of absorption, distribution, metabolism, protein binding and elimination may be different for the 2 enantiomers, leading to interindividual variability in clinical response and drug toxicity.