FLUORESCENCE STUDIES OF THE BINDING OF 2 NATURAL ALKALOIDS (CINCHONINE AND CINCHONIDINE) WITH BETA-LACTOGLOBULIN

The binding to the transport protein beta-lactoglobulin (beta-LG) of t he natural alkaloids stereoisomers, cinchonine and cinchonidine, has b een investigated in a pH 7.5 buffer solution by fluorescence spectrosc opy. The large decrease of beta-LG fluorescence brought about by addit ion of cinchonine and cinchonidine has been correlated to an increase of the complex emission, indicating an efficient energy transfer. The complex affinity constants have been evaluated. The results clearly sh ow that only one binding site is affected in the dimeric protein, and that the affinity of cinchonine for beta-LG is much more important tha n that of cinchonidine.