14C radiolabeling of proteins to monitor biodistribution of ingested proteins

Laura D.R. Davis, William J. Spencer, Van Thong Pham, Tonya L. Ward, David R. Blais, David R. MacK, Harvey Kaplan, Illimar Altosaar

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The economical preparation of microgram quantities of 14C- labeled proteins by in vacuo methylation with methyl iodide is described. The 14C radiolabeling was achieved by the covalent attachment of [ 14C]methyl groups onto amino and imidazole groups by reaction in vacuo with [14C]methyl iodide. The method was tested by investigating the biodistribution of 14C in rats that were fed 14C-labeled human soluble cluster of differentiation 14 (CD14) protein, a receptor for bacterial lipopolysaccharide. Two other control proteins, bovine serum albumin (BSA) and casein, were also labeled with 14C and used for comparative analysis to determine the following: (i) the efficacy and cost efficiency of the in vacuo radiolabeling procedure and (ii) the extent of incorporation of the 14C label into the organs of orogastrically fed 10-day-old Sprague-Dawley rats. [14C]BSA, [ 14C]casein, and [14C]CD14 were individually prepared with specific radioactivities of 34,400, 18,800, and 163,000 disintegrations per minute (dpm)/μg, respectively. It was found that the accumulation of 14C label in the organs of [14C]CD14-fed rats, most notably the persistence of 14C in the stomach 480 min postgavage, was temporally and spatially distinct from [14C]BSA and [ 14C]casein-fed rats.

Original languageEnglish (US)
Pages (from-to)57-61
Number of pages5
JournalAnalytical Biochemistry
Issue number1
StatePublished - Mar 1 2011


  • Carbon-14 methylated proteins
  • Digestive fate of peptides
  • In vacuo conjugation
  • Radiolabeled tracer proteins
  • Trimethylated lysine


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