This material readily decarboxylates to give indoxyl, which oxidizes in air to form indigo. Bacteria in the urine produce the enzyme indoxyl phosphatase. Indoxyl sulfate is one of the better characterized uremic toxins. Indoxyl is obtained from indican, which is a glycoside. This highly sensitive melt produces indoxyl, which is subsequently oxidized in air to form indigo. There, indole is converted to indoxyl sulfate, which is then excreted in the urine. The X from indoxyl may be the source of the X in the X-gal contraction. Indoxyl can be found in urine and is titrated with Obermayer's reagent. Indoxyl is isomeric with oxindol and is obtained as an oily liquid.