Summary
      
      Proteins are macromolecules very abundant in living organisms, that are involved in various vital functions. In particular, transport  proteins (such as HSA and AAG), serve as a vehicle for the distribution of a wide variety of endogenous and exogenous substances in blood. 
      Flurbiprofen (FBP) is a NSAID of the 2-arylpropiónic acid family. This drug is carried by ASH, although AAG may also be involved in the process. Methyl ester of FBP is a prodrug, which also interacts with both proteins. The major phase II metabolite of FBP is its glucuronide that, it also binds to HSA although to a lesser extent
      The study of drug/protein interactions is important to understand the biodistribution, metabolism, disposal and pharmacological effect of drugs in the body. A number of techniques are available to address these issues. Recently laser flash photolysis has been used for this purpose, showing that the triplet excited states are very sensitive to the surrounding environment ; therefore, they can be used as a probes for the study of drug-protein binding. 
      With this background, the main goal of the present work is to extend the previous studies of this group to serum albumins of other species as well as to other transport  proteins such as AAG. 
      Thus, the interaction of FBP, FBPMe and FBPGluc with albumins of various species (rabbit, dog, pigs, sheep and rat) was undertaken to establish comparisons with the case of HSA. This parallel experiments have been carried out with both enantiomers of each compound, to detect a possible stereodifferentiation in their interaction with the proteins. An appropiate analysis of the decays traces revealed significant species dependent differences in the binding of the drug or its derivatives to SAs, both in the number of binding sites, and in the triplet lifetimes within the protein. 
      The glucuronidase activity of different albumins on FBPGluc has also been investigated, taking advantage of the different triplet lifetimes of FBPGluc and FBP within the protein binding sites. An interesting observation is that hydrolysis takes actually place inside the protein, at physiological temperature. 
      Another interesting application of the methodology is the interaction of the substrates with HSA and AAG present  simultaneously. A regression analysis of the decay traces,  provides valuable information about the binding sites of both proteins.  
      In conclusion, a novel method for the straightforward determination of enantiomeric compositions is presented here. It is based on transient spectroscopy, exploiting the differences in triplet lifetimes within serum albumins for chiral recognition. The method is fast and simple, as it requires just one measurement per sample to provide accurate results. It is highly sensitive and is appropriate for analysis of minute (µg) amounts. As further advantages, it avoids substrate derivatization as well as chromatographic separation and does not depend on the specific rotation on the target compound. All together, the above reasons make this LFP-based approach a very complementary tool to the existing techniques.