Urea is the conspicuous end-product of nitrogenous metabolism in the higher organisms. The theories to account for its origin have undergone successive modifications from decade to decade in harmony with the latest chemical evidence available at successive intervals. Thus the hypotheses of the genesis of urea through oxidative synthesis and in other ways directly from proteins have gradually been abandoned. At the present moment, in the light of what is known respecting the rôle of amino-acids in the disintegration of protein and its metabolism in the body, urea is no longer regarded as a product of the entire molecule. The nitrogenous groups of the amino-acids are split off from the rest of these complexes, perhaps by enzymatic deamination. From these nitrogenous fragments, urea arises.
With respect to the place or tissues in which this reaction proceeds, opinion has likewise been vacillating. Of late there has been a tendency to assign
IS UREA FORMED IN THE MUSCLES? JAMA. 1917;LXIX(21):1791–1792. doi:10.1001/jama.1917.02590480045019
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