In enzymology, 3-hydroxybutyrate dehydrogenase is an enzyme that catalyzes the chemical reaction: -3-hydroxybutanoate + NAD+ ⇌ {\displaystyle \rightleftharpoons } acetoacetate + NADH + H+Thus, the two substrates of this enzyme are -3-hydroxybutanoate and NAD+, whereas its three products are acetoacetate, NADH, and H+. Wikipedia