This radical, a macromolecule, had formula C20 H31 N5 O12 , and was known as protein. The variations in albuminous substances were attributed to peripheral bonds of protein to sulfur and/or phosphorus. Justus Liebig and his students sought to determine the structure of proteins, but until the methods of Emil Fischer and Franz Hofmeister became available, the amino acid decompositions were unknown.Hubert Bradford Vickery (1942) "Liebig and the Proteins", Journal of Chemical Education
