ID 4.2.1.27 DE acetylenecarboxylate hydratase. AN acetylenemonocarboxylate hydratase. AN alkynoate hydratase. AN malonate-semialdehyde dehydratase. CA 3-oxopropanoate = H2O + propynoate. CC -!- The reaction is effectively irreversible, favoring oxopropanoate CC (malonic semialdehyde) and its tautomers. CC -!- Also acts on but-3-ynoate forming acetoacetate. CC -!- The mechanism appears to involve hydration of the acetylene to CC 3-hydroxypropenoate, which will spontaneously tautomerize to CC 3-oxopropanoate. CC -!- It is thus analogous to EC 4.1.1.78 in its mechanism. CC -!- Formerly EC 4.2.1.71. //