Excerpt from The Biochemical Journal, 1913, Vol. 7: Edited for the Biochemical Society
The whole question of the course of the breakdown of the protein molecule within the tissues is one of the most obscure in physiology. We have now a fairly good idea of the form in which the protein is absorbed from the lumen of the intestine but its immediate fate is still unknown. Apparently however definite evidence is now collecting [Folin, 1912] in support of the view that no immediate synthesis, analogous to that of fat, takes place. Unquestionably, irrespective of the form in which the protein material is conveyed to the tissues, there is, soon after the ingestion of food, a fairly complete disintegration of the protein molecule as evidenced by the increase in the output of nitrogenous substances in the urine. Of course it might be maintained, as it has been, that this material arises not from the newly ingested material but from "effete" protoplasm broken down and discarded when a new supply of repair material is available. If this be so then the material excreted ought to bear some definite percentage relationship to the normal protein of the body, for example the ratio of sulphur to nitrogen in the urine should approximate to that of the average tissue as obtained say by the study of the sulphur and nitrogen ratio in complete starvation.
It was thought that, by a careful study of the ratios of S:N after feeding with specially chosen foodstuffs, light might be thrown on: -
(1) The rate of protein catabolism.
(2) The nature of the material catabolised.
Previous Work.
Little work has been carried out in this field probably because of the fact that until recently the difficulty of carrying on a long series of sulphur analyses was considerable. Since the introduction of the very excellent and rapid method of S. R. Benedict this difficulty has largely disappeared.
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