Evidence for histidine in the active sites of ficin and stem-bromelain.
1. Ficin and stem-bromelain are irreversibly inhibited by 1,3-dibromoacetone, a reagent designed to react first with the active-site cysteine residue and subsequently with a second nucleophile. Evidence is presented that establishes that a histidine residue is within a 5A locus of the active-site cysteine residue in both enzymes. The histidine residue in both enzymes is alkylated at N-1 by dibromoacetone. It is suggested that, as with papain, the thiol and imidazole groups act in concert in the hydrolysis of substrates by these enzymes. 2. The inhibition of thiol-subtilisin with 1,3-dibromoacetone is shown to be due to the alkylation of a cysteine residue only.
D000096:Acetone; D000478:Alkylation; D001963:Bromelains / Q000037:antagonists & inhibitors; D001966:Bromine; D055598:Chemical Phenomena; D002621:Chemistry; D002850:Chromatography, Gel; D003545:Cysteine; D010450:Endopeptidases; D006639:Histidine; D011480:Protease Inhibitors
D011480:Protease Inhibitors; D000096:Acetone; D006639:Histidine; D001963:Bromelains; D010450:Endopeptidases; D003545:Cysteine; D001966:Bromine