Metabolism and the Occurrence of d(−)Glutamic Acid in Tumour Proteins

Abstract

SEVERAL investigators¹, using isotope techniques, have failed to reproduce Kögl's results on the d(−)glutamic acid content of tumour proteins. All such experiments were based on the hydrolysis of tumour proteins with concentrated hydrochloric acid. Kögl tried to explain the discrepancies as due to differing methods of hydrolysis²; but strangely enough, Kögl's feeding experiments have never been repeated. In 1940, Kögl was able to isolate, after hydrolysis, d(−)glutamic acid from the fæces of a dog which had been fed with Brown–Pearce tumour tissue; in 1948, he obtained in a similar way pure d-pyrrolidonic acid after feeding tumour protein³ using the method of Ratner, that is, extraction of the urine with ethyl acetate at pH 2 and precipitation with barium⁴. No objections can be raised to these methods.