4-Hydroxycinnamoyl-CoA Hydratase/lyase (HCHL)—An Enzyme of Phenylpropanoid Chain Cleavage fromPseudomonas

The enzyme 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL), which catalyzes a hydration and two-carbon cleavage step in the degradation of 4-hydroxycinnamic acids, has been purified and characterized fromPseudomonas fluorescensstrain AN103. The enzyme is a homodimer and is active with three closely related substrates, 4-coumaroyl-CoA, caffeoyl-CoA, and feruloyl-CoA (Kmvalues: 5.2, 1.6, and 2.4 μM, respectively), but not with cinnamoyl-CoA or with sinapinoyl-CoA. The abundance of the enzyme reflects a low catalytic center activity (2.3 molecules s−1at 30°C; 4-coumaroyl-CoA as substrate).