Abstract: An object of the present invention is to provide a method for synthesizing, in a cell-free protein synthetic system using a wheat germ extract, a protein of interest that is labeled in an amino-acid-selective manner. The present invention provides a method for carrying out a translation reaction of a protein of interest under a condition whereby a metabolic reaction of alanine to aspartic acid and glutamic acid, a metabolic reaction of aspartic acid to glutamic acid or a metabolic reaction of glutamic acid to aspartic acid and/or glutamine is inhibited, while the protein synthesis is not inhibited, when alanine, aspartic acid or glutamic acid of the protein of interest is labeled with a stable isotope in a cell-free protein synthetic system containing a wheat germ extract.

Abstract: An object of the present invention is to provide a means for highly efficiently or quickly evaluating or determining the three-dimensional structure of a protein by conducting multidimensional multinuclear NMR measurement without performing a step of separating and purifying the synthesized labeled protein from other labeled proteins. The present invention provides a method for analyzing proteins, which comprises: synthesizing a protein of interest under conditions in which 90% or more of the synthesized labeled proteins constitute the protein of interest, when proteins are synthesized using a nucleic acid encoding the protein of interest as a template and also using substrate amino acids, a part or all of which have been labeled in such a way that NMR measurement is possible; and performing the NMR measurement using the above-described labeled proteins.