The Metabolism of Sulfur
نویسنده
چکیده
The mechanism of the intermediary metabolism of the more complex amino-acids still remains obscure. It is generally CODceded that, as far as concerns the a-amino group, deamination is accompanied by oxidation with the formation of cu-keto or cr-hydroxy derivatives of the amino-acids. While the manner of oxidation of the cyclic portions of such amino-acids as contain the benzene or other rings is not fully known, it is usually considered that their oxidation is involved in the further oxidation of the ketoor hydroxy-acids, products of deamination. Thus, phenylalanine in moderate amounts is readily and completely oxidized in the body, while phenylpropionic acid (1) is oxidized only to benzoic and cinnamic acids, and eliminated in conjugation with glycocoll without further oxidation. Phenyllactic and phenylpyruvic acids (2), both products of the normal deamination of phenylalanine, are completely oxidized, while p-phenylalanine (3,4) and phenylserine (3), and their respective deamination products, /3-hydroxyphenylpropionic acid and phenylglyceric acid (3) undergo no oxidation of the benzene ring. Our knowledge of the normal path of oxidation of the sulfurcontaining amino-acid, cystine, is even more hazy. The conversion of cystine through cysteinic acid to taurine in vitro has been effected by Friedmann (5). However, even if it is to be considered as definitely proved that taurine originates in viva from cystine (6,7, S), the fact that the sulfur in taurine itself is oxidized to sulfates with difficulty, if at all (9, 10, ll), in the animal body, makes it improbable that taurine is primarily concerned in the intermediary metabolism of cystine.
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