William Rose and the Essential Amino Acids, 1935 to 1955
William Rose's casein hydrolysate led him to histidine as a dietary essential in 1924. His 1935 work identified threonine, the last amino acid found in proteins, and his human trials set the adult essentials at eight.
Threonine was the last amino acid found to be a universal part of proteins, and William Cumming Rose's group identified it in 1935. The path there ran through a casein hydrolysate, a 1924 histidine finding, and years of feeding rats purified amino acids. Of the 22 amino acids known in proteins, only eight are essential for adult humans, and [the National Academy of Sciences memoir on Rose](https://www.nasonline.org/wp-content/uploads/2024/06/rose-william.pdf) traces how that number was reached. ## A casein hydrolysate pointed to histidine Rose's first clear finding came from a side project. At the University of Texas he prepared a casein hydrolysate to study arginine as a possible precursor of creatine. After he moved to Illinois, he removed arginine and histidine from it. Rats lost weight on the treated hydrolysate, but they responded when histidine was added, and arginine could not replace it. The memoir calls the difference in response "little short of sensational" and says his 1924 report was the first on an indispensable amino acid. Osborne and Mendel had shown the same principle earlier with a different protein. Their rats failed to grow on corn protein zein until tryptophan and lysine were added, and the memoir calls that the first clear-cut evidence that individual amino acids might be required by animals. ## The missing growth factor was threonine Rose then built diets from purified amino acids instead of protein. A diet with 19 highly purified amino acids would not support growth, so his group searched for the growth essential that proteins still contained. The breakthrough came in a 1935 paper by R. H. McCoy, C. E. Meyer and Rose, which reported the isolation and identification of a new essential amino acid. The memoir gives its structure as alpha-amino-beta-hydroxy-n-butyric acid, and it says the purified compound was the first to rear animals on purified amino acids as the only nitrogen source. The paper's own sentence, quoted on a plaque in the memoir, reads: "The data demonstrate conclusively that the crystalline compound is the new essential we have been endeavoring to isolate for several years." H. E. Carter later synthesized the four isomers of that acid. Only one form supported rat growth, and it became L-threonine. The memoir cites Carter's 1979 account in *Federation Proceedings*. ## Which amino acids can the body make? The method was simple in principle. Remove one amino acid at a time from a purified diet and see whether growth fails. In rats, Rose's group found that ten of the 22 amino acids in proteins were indispensable dietary components: histidine, isoleucine, leucine, threonine, lysine, methionine, phenylalanine, tryptophan, valine and arginine. Arginine was the exception. Rats kept gaining weight without it, which the memoir reads as a sign that the body makes it, but slowly. Essential meant something specific in this work: an amino acid counted as essential when its removal caused a failure of normal growth in the rat. In a canine study, the amino acids dispensable for growing rats were also dispensable for adult dogs, judged by nitrogen equilibrium, according to the memoir. ## Eight essential amino acids for adults Rose moved to people in 1942. Healthy male graduate students ate diets built from corn starch, sucrose, defatted butter fat, corn oil, salts, vitamins and purified amino acids. Nitrogen balance compares the nitrogen taken in with the nitrogen lost in urine and feces, and the team measured both. The 12 amino acids that animals could do without were also dispensable for people. Removing the other ten one at a time caused negative nitrogen balance for isoleucine, leucine, tryptophan, lysine, methionine, phenylalanine, threonine and valine. Arginine made no difference, and histidine was the surprise, since subjects without it kept normal nitrogen balance. The memoir concludes that only eight amino acids are essential for the adult human. The later students were paid a dollar a day, and the memoir says they were grateful for the free rations and for seeing their initials in print. The rat and human lists differ mainly in histidine, which rats needed and adults did not, and in arginine, which rats could make only slowly. The memoir also cites a 1992 account in which the first two human subjects recalled the early experiments fifty years later. The trials ran into the early 1950s and produced 16 papers in the *Journal of Biological Chemistry*. They proposed minimum daily levels from 0.25 grams of tryptophan to 1.1 grams for several other amino acids, with twice those amounts as a safe margin. Rose's 1949 *Federation Proceedings* paper, "Amino acid requirements of man," is indexed in [PubMed](https://pubmed.ncbi.nlm.nih.gov/794768/) as a 1976 *Nutrition Classics* reprint ([DOI](https://doi.org/10.1111/j.1753-4887.1976.tb05679.x)). ## Protein quality became a score Rose's requirement data made it possible to judge a protein's quality for people from its amino acid makeup, instead of relying on animal tests alone, according to the memoir. The FAO/WHO expert consultation in 1991 later endorsed the protein digestibility-corrected amino acid score, or PDCAAS, as the most suitable routine method for human protein quality ([Millward, 2012](https://doi.org/10.1017/S0007114512002462); [Gilani, 2012](https://doi.org/10.1017/S0007114512002383)). Rose's creatine work is a separate thread. He studied creatine and creatinine with Lafayette Mendel at Yale, and the memoir dates those studies to 1911. Our [creatine history](/blog/history/history-of-creatine-from-meat-extract-to-sports-shelf) follows that compound on its own path. For the metabolism side, our [mitochondrial health guide](/health/mitochondrial-health-complete-guide) and [NAD longevity guide](/health/nad-longevity-complete-guide) are the places to start. The 1942 diet came with a large brown candy containing concentrated liver extract, sweetened and flavored with peppermint oil. The memoir says it provided "a never-to-be-forgotten taste," which is the detail most worth keeping from the human trials. **Next reads** - [Mitochondrial health complete guide](/health/mitochondrial-health-complete-guide): the pillar for the metabolism context here. - [Creatine: From a Meat Extract in 1832 to the Sports Shelf](/blog/history/history-of-creatine-from-meat-extract-to-sports-shelf): the sibling history of the compound Rose studied with Mendel. ### Related reading - [carnitine history from meat extract to fat transport](/blog/history/history-of-carnitine-from-meat-extract-to-cellular-fuel) - [how tryptophan became an outbreak and niacin story](/blog/history/history-of-tryptophan-from-casein-to-the-1989-recall)