Abstract
THE biological importance of a protein is dependent on the extent to which it is able to supply the amino-acids which the animal cannot synthesize for itself. Willcock and Hopkins (1906–7) showed that young mice, fed on a diet in which zein was the sole protein, lost weight and died in about 17 days. The addition of tryptophan to the diet enabled the mice to survive for longer periods, although they continued to lose weight. In 1914, Osborne and Mendel repeated the experiments and found that, in growing rats, the addition of tryptophan enabled the animals to maintain their normal weights, and that with the further addition of lysine normal growth was restored. Tryptophan and lysine were therefore regarded as essential amino-acids, the list of which was afterwards extended to include histidine, threonine, valiae, phenylalanine, leucine, isoleucine and methionine or possibly cysteine. The discovery of threonine by Rose (1931) was the direct outcome of experiments involving the feeding to rats of synthetic mixtures of all the amino-acids known at that time. The rats failed to grow, and Rose concluded that proteins probably contain an unknown amino-acid, which was afterwards isolated and identified as a-amino-p-hydroxy-n-butyric acid (threonine).
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DIXON, T. Biochemical Importance of Individual Amino-Acids. Nature 153, 289 (1944). https://doi.org/10.1038/153289a0
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DOI: https://doi.org/10.1038/153289a0
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