Cell‐free production and stable‐isotope labeling of milligram quantities of proteins

We have improved the productivity of an Escherichia coli cell-free protein synthesis system. First, creatine phosphate and creatine kinase were used as the energy source regeneration system, and the other components of the reaction mixture were optimized. Second, the E. coli S30 cell extract was condensed by dialysis against a polyethylene glycol solution to increase the rate of synthesis. Third, during the protein synthesis, the reaction mixture was dialyzed against a low-molecular-weight substrate solution to prolong the reaction. Thus, the yield of chloramphenicol acetyltransferase was raised to 6 mg/ml of reaction mixture. Stable-isotope labeling of a protein with 13C/15N-labeled amino acids for NMR spectroscopy was achieved by this method.