A bifunctional enzyme which catalyzes the dehydration of anhydrofructose into ascopyrone M, and the isomerization of ascopyrone M into microthecin. 1,5-anhydro-D-fructose = H2O + microthecin Binds 3 Zn(2+) ions per subunit. Optimum pH is 5.8 for dehydration of anhydrofructose and 6.8 for isomerization of ascopyrone M. Carbohydrate metabolism; 1,5-anhydro-D-fructose degradation. Homodimer.