 Early nutritional scientists such as the German Carl von <unk> believed that protein was the most important nutrient for maintaining the structure of the body , because it was generally believed that " flesh makes flesh . " Karl Heinrich <unk> extended known protein forms with the identification of <unk> acid . At the Connecticut Agricultural Experiment Station a detailed review of the vegetable proteins was compiled by Thomas Burr Osborne . Working with Lafayette <unk> and applying <unk> 's law of the minimum in feeding laboratory rats , the <unk> essential amino acids were established . The work was continued and communicated by William <unk> Rose . The understanding of proteins as polypeptides came through the work of Franz <unk> and Hermann Emil Fischer . The central role of proteins as enzymes in living organisms was not fully appreciated until 1926 , when James B. Sumner showed that the enzyme <unk> was in fact a protein . 
