The Fate of Proline in the Animal Body,

Since nothing appeared to be known as to the fate of proline in the animal body, it seemed desirable to make some experiments in the hope that some light might be thrown upon the changes which this amino-acid may undergo. As a first step in the investigation, observations were made on the behavior of proline when added to blood used for perfusing a surviving dog’s liver, using essentially the method which has been so successfully applied by Embden, and secondly, an examination was made of the influence of proline on the glycosuria and acidosis of dogs under the influence of phlorhizin. Proline, when added to blood used for perfusing a surviving dog’s liver, leads to no increase in the normal formation of acetoacetic acid, nor is the acetoacetic acid excretion of glycosuric animals markedly increased by the administration of proline. It is clear, therefore, that proline is not to be classed with phenylalanine, tyrosine or leucine in having acetoacetic acid for a common catabolic path. On the other hand, administrations of proline to the glycosuric animal was found to result in a marked increase in sugar output, so that it would appear that proline should be grouped with glutamic and aspartic acids, alanine and glycine, all of which have been shown by Lusk,l Ringer and others to be capable of furnishing glucose. The formation of glucose from proline must necessarily involve disruption of the ring and it is of interest to recall the similarity in structure of the amino-acids, proline, glutamic acid and orni-