Labeling of Human Serum Albumin with Stable Isotope of Bromine; an in Vitro Study

Background: possibility to trace-label albumin with isotopesresults in information concerning its synthesis, breakdown, anddistribution in the intra and extra cellular spaces. the iodinationof albumin is a widespread procedure used in scientificstudies,bromine not only is more reactive and less expensive than iodine,but bonds more easily with many elements. therefore, itcould be a suitable tracer in labeling procedures. the presentstudy was designed to represent a method for labeling humanserum albumin (hsa) with stable isotope of bromine.methods: in the present study, the labeling of hsa by use ofstable isotope of bromine c9br) has been sought through a seriesof preliminary experiments including iodination of bovineserum albumin (bsa) and iodination and bromination of bsa.the experiments were basically designed according to that ofme conahey and dixon in 1966. all measurements have beenobtained by inductive coupled plasma mass spectrometry(icpims). twenty protein solutions, each having 50 mg hsadissolved in 10 ml of 0.05 m buffer (ph 7.0) were prepared. aseries of calculated amounts of pure bromine was added directlyto each sample. each sample was placed in a crystallizing dishcontaining crushed ice to keep the reactants cold. after dialysisand final preparation of the samples, the intensities of brominein the samples were measured.results: data indicated the maximum presence of bromine inhsa samples in a ratio of 40 atoms of bromine to each moleof hsa. after dialysis, sample analysis showed that on average,about 65% of the bromine was really bound to the hsamolecules. this finding indicates that about 26 atoms of brominewere bound to each hsa molecule . data analyzed bysimple linear regression method. results showed that each ugincrease in dose leads to 0.002 unit increase in the mean ofmole ratio of pure bromine (br2)/hsa (p=0.001).conclusion: the present study has unique specifications inthat almost all of the labeling procedures of plasma proteinshave used other elements rather than bromine and mostly radioactiveisotopes instead of stable isotopes. the present papershowed a method for about minimum as well as maximumbromination of hsa (0.05 atoms- 26 atoms) , within certainlimits of experimental conditions. by this method, one canexactly determine how much bromine should be used to obtaina certain desired mole ratio of br2/hsa with no, or at leastminimal, alteration of protein behavior.