Description:
<jats:title>Abstract</jats:title><jats:p><jats:italic>The putative hydrolase gene</jats:italic> bhp <jats:italic>from the balhimycin biosynthetic gene cluster has been cloned and overexpressed in</jats:italic> Escherichia coli<jats:italic>. The corresponding enzyme Bhp was purified to homogeneity by nickel‐chelating chromatography and characterized. Although Bhp has sequence similarities to hydrolases with “haloperoxidase”/perhydrolase activity, it did not show any enzymatic activity with standard “haloperoxidase”/perhydrolase substrates (e.g., monochlorodimedone and phenol red), nonspecific esterase substrates (such as</jats:italic> p<jats:italic>‐nitrophenyl acetate,</jats:italic> p<jats:italic>‐nitrophenyl phosphate and</jats:italic> S<jats:italic>‐thiophenyl acetate) or the model lactonase substrate dihydrocoumarin. However, Bhp could be shown to catalyse the hydrolysis of</jats:italic> S<jats:italic>‐β‐hydroxytyrosyl‐</jats:italic>N<jats:italic>‐acetyl cysteamine thioester (β‐OH‐Tyr‐SNAC) with 15 times the efficiency of</jats:italic> S<jats:italic>‐<jats:sc>L</jats:sc>‐tyrosyl‐</jats:italic>N<jats:italic>‐acetyl cysteamine thioester (<jats:sc>L</jats:sc>‐Tyr‐SNAC). This is in agreement with the suggestion that Bhp is involved in balhimycin biosynthesis, during which it was supposed to catalyse the hydrolysis of β‐OH‐Tyr‐</jats:italic>S<jats:italic>‐PCP (PCP=peptidyl carrier protein) to free β‐hydroxytyrosine (β‐OH‐Tyr) and strongly suggests that Bhp is a thioesterase with high substrate specificity for PCP‐bound β‐OH‐Tyr and not a “haloperoxidase”/perhydrolase or nonspecific esterase.</jats:italic></jats:p>