Oxidation of Methionine Sulfur in Vivo

The oxidation of methionine sulfur in the living animal appears to take place in both the d- and Z-forms. Among the products of this oxidation, notably sulfate, thiosulfate, and taurine have been isolated. 

The oxidation of methionine sulfur to sulfate in humans, after ingestion of the Z-form was observed for the first time by Mueller (88). It has since been encountered in a number of other cases in rabbits, after ingestion or subcutaneous or intravenous injection of the ZZ-form (138) in d( after ingestion of the dZ-derivative (94) and in humans after ingestion of either the Z-, or the dZ-form (84). This oxidation is quantitatively important, since the sulfate formed represents 60 to 70% (94) or even sometimes 100% of the introduced organic sulfur. 

The formation of thiosulfate after injection of dZ-methionine has been observed in rabbits (49) which were kept on an extremely low sulfur diet. Of the 378 mg. of methionine sulfur introduced, 0.6%. was recovered from the urine after a 48-hour interval. This amount, though very small, is nevertheless significant. It bears out the fact that thiosulfate forms an intermediary compound in the oxidation of sulfur to sulfate, as we shall see on page 400. 

Regarding the oxidation of methionine sulfur to taurine, the results of the experiments by Virtue and Doster-Virtue (134) with dogs have shown the existence of the oxidation reaction to be highly probable. The animals were first given a diet to deplete their taurine reserves a bile fistula operation was performed then ingestion of dZ-methiouine and cholic acid simultaneously was forced. This ingestion produces a decided increase in the quantity of excreted taurocholic acid. The absolute proof of the oxidation of sulfur of methionine to taurine has been furnished by Tarver and Schmidt 

OXIDATION MECIIANISM.S OF METHIONINE SULFUR 1. Does Direct Oxidation of Methionine Sulfur Exist  

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