ID 5.4.99.14 DE 4-carboxymethyl-4-methylbutenolide mutase. AN 4-methyl-2-enelactone methyl-isomerase. AN 4-methyl-3-enelactone methyl isomerase. AN 4-methylmuconolactone methylisomerase. CA 4-carboxymethyl-4-methylbut-2-en-1,4-olide = 4-carboxymethyl-3-methylbut- CA 2-en-1,4-olide. //