Thiazole tautomerase (, tenI (gene)) is an enzyme with systematic name 2-(2-carboxy-4-methylthiazol-5-yl)ethyl phosphate isomerase. This enzyme catalyses the following chemical reaction
The enzyme catalyses the irreversible aromatization of the thiazole moiety of 2-[(2R,5Z)-2-carboxy-4-methylthiazol-5(2H)-ylidene]ethyl phosphate.