Editing Essential amino acid (section)

==Complete proteins in non-human animals==
Scientists had known since the early 20th century that rats could not survive on a diet whose only protein source was [[zein]], which comes from [[maize]] (corn), but recovered if they were fed [[casein]] from cow's milk. This led [[William Cumming Rose]] to the discovery of the essential amino acid [[threonine]].<ref>{{cite journal |vauthors=Rose WC, Haines WJ, Warner DT, Johnson JE |title=The amino acid requirements of man. II. The role of threonine and histidine |journal=The Journal of Biological Chemistry |volume=188 |issue=1 |pages=49–58 |pmid=14814112 |year=1951|doi=10.1016/S0021-9258(18)56144-5 |doi-access=free }}</ref> Through manipulation of rodent diets, Rose was able to show that ten amino acids are essential for rats: [[lysine]], [[tryptophan]], [[histidine]], [[phenylalanine]], [[leucine]], [[isoleucine]], [[methionine]], [[valine]], and [[arginine]], in addition to threonine. Rose's later work showed that eight amino acids are essential for adult human beings, with histidine also being essential for infants. Longer-term studies established histidine as also essential for adult humans.<ref>{{cite journal |vauthors=Kopple JD, Swendseid ME |date=May 1975 |title=Evidence that histidine is an essential amino acid in normal and chronically uremic man. |journal=J Clin Invest |volume=55 |issue=5 |pages=881–891 |pmid=1123426 |pmc=301830 |doi=10.1172/JCI108016}}</ref>