β-Hydroxydecanoyl Thioester Dehydrase

β-Hydroxydecanoyl thioester dehydrase of Escherichia coli has been purified 1200-fold. Its molecular weight is estimated at 28,000 by gel filtration and by zone sedimentation analysis. At all stages of purification, the enzyme catalyzes the dehydration of β-hydroxydecanoate to a mixture of β,γ- and α,β-decenoates, α,β predominating; the β,γ:α,β product ratio does not change with purification. Several additional lines of evidence are presented which argue that a single enzyme is responsible for the formation of both isomeric decenoates. Attempts to alter the activity and β,γ:α,β specificity of the enzyme have proved unsuccessful. The enzyme is active over a wide pH range and is insensitive to sulfhydryl poisons. The presence of a thioesterase activity in E. coli is noted.