KETOISOCAPROATE CONTAMINATION ERRORS IN PROTEIN-SYNTHESIS DETERMINATIONS USING L-[1-C-14]LEUCINE

Protein synthesis rate determinations in vivo using L-[1-C-14]-leucine may be underestimated because of contamination by radioactive ketoiso caproate (KIC) resulting from leucine metabolism. The aim of this work was to set up a reliable method to determine the KIC/leucine radioact ivity ratio in protein-free homogenates, and to apply it to study the extent of the protein synthesis ratio error due to KIC contamination. Cation-exchange chromatography using Dowex AG 50W-X8 resin was used to separate KIC from leucine, eluting KIC with water and leucine with 4 M ammonia. The errors found in the protein synthesis ratio were 6.20% in liver and 2.34% in jejunum.