Assessment of counting efficiencies for labeled protein and other macromolecules in filter disk assays.
A several-fold greater counting efficiency is observed for protein labeled with [3H]leucine than for free [3H]leucine using a conventional filter disk assay. A similar, though less marked, effect is noted for 14C-labeled molecules. These results are comparable to those reported by others for counting efficiencies of labeled DNA and deoxynucleotides and illustrate the generality of this effect with regard to macromolecules and their low-molecular weight precursors. This phenomenon, presumably due to differences in the distribution of large and small molecules within filters, gives rise to errors in the quantitation of macromolecule synthesis if a counting efficiency identical to that of the precursor is assumed to apply. A convenient method for determining counting efficiencies of various molecules bound to filters is presented which eliminates this problem.
Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge 02139, USA.
E B
EB
Albright
T S
TS
Nowak
H N
HN
Munro
D002250:Carbon Radioisotopes; D002474:Cell-Free System; D005374:Filtration / Q000295:instrumentation; D066298:In Vitro Techniques; D007930:Leucine / Q000032:analysis; D014176:Protein Biosynthesis; D011506:Proteins / Q000032:analysis*; D012588:Scintillation Counting / Q000379:methods* / Q000706:statistics & numerical data; D014316:Tritium
D002250:Carbon Radioisotopes; D011506:Proteins; D014316:Tritium; D007930:Leucine