Is cystin synthesized in the animal body?

Abstract

We undertook a series of experiments in order to determine which of the amino acids occurring in proteins were possible of synthesis in the animal organism. According to Abderhalden, any of the aliphatic amino acids should be synthesized, but probably none of the hetero-cyclic or aromatic acids. It has already been shown that glycocoll can be built in the animal organism 1 2 and we have previously shown 3 that glycocoll and also glutamine can be synthesized in the human body at the expense of nitrogen which would otherwise be found in the urea portion of the urine, and peculiarly that both acids are prepared simultaneously as well as singly.

Recent feeding experiments have shown that cystin is a necessary amino acid in protein if growth or maintenance of body weight is desired, therefore indicating that neither cystin nor cystein is synthesized in the organism.

In 1879 Baumann 4 and Jaffe 5 independently discovered that brom-benzene fed to dogs is detoxicated by joining the cystein molecule followed by an acetylation of the amino group of the latter.

We thought that perhaps under these conditions of brom-benzene intoxication it might be possible for the organism to synthesize cystein, although it was unable to do so for dietary purposes.

Kopfhammer 6 at this time published a paper showing that on a non-protein diet the dog is unable to synthesize cystein, although at the same time fed brom-benzene. We then undertook three series of experiments. In the first we placed the dog on a carbohydrate diet and fed each day brom-benzene. Besides this on the first two days we fed sodium sulphate, the second two days we fed taurine, the next two days calcium sulfate, the following two days sodium sulphocyanate, then following this ethylamino mercaptan, and finally cystin.