A new in vivo metabolite of vitamin D3: 1,25,26-trihydroxyvitamin D3

The enzymatic conversion of 5-methylthioribose to methionine and its deaminated derivatives, 2-keto-4-methylmercaptobutyric acid and 2-hydroxy-4-methylmercaptobutyric acid by cell-free extracts of $\text{Enterobacter}\text{aerogenes}$ has been demonstrated. ¹⁴C-Labeled methionine was isolated from incubation mixtures with 5-methylthioU-¹⁴C]ribose. The carbohydrate part of this compound furnishes at least part, if not all, of the four carbon chain of methionine.