Bromelain active site

In the course of investigations using 4-chloro-7-nitrobenzofurazan as a reactivity probe for identifying the active sites of a number of enzymes such as papain, ficin, and bromelain, the intermediacy of Meisenheimer adducts derived from direct attack of thiolate groups located in the protein has been assumed on the basis of the spectral changes accompanying the process of replacement of the chloro group.232,233... 

Husain, S. S., and Lowe, G. (1968) Evidence for histidine in the active sites for ficin and stem-bromelain. Biochem. J. 110, 53. 

His1 0 and orients it for its catalytic function [54], The putative catalytic thiolate-imldazollum pair at the active site of bromelain is thus, by comparison of the amino acid sequence of bromelain with other cysteine protein ases, likely to have a different conformation from that in (he cysteine proteinases (hat aie tightly inhibited by cystatin [45]. Bromelain also distinguishes itself from other cysteine protein ases by its slow inhibition by the irreversible inhibitor of cysteine oroteinases E-64 rW-ft 3-fraw-cari)OKVOxiran-2 BrboiwlVL-leucvn-amido 4-... 

S. S. Hussain and G. Lowe. The amino acid sequence around the active-site cysteine and histidine residues of stem bromelain. Biochem. J. 7/7 341 (1970). 

Cysteine endopeptidase Cysteine in the active site Papain, ficin, bromelain, cathepsin B... 

An exceptionally reactive serine residue has been identified in a great number of hydrolase enzymes, e. g., trypsin, subtilisin, elastase, acetylcholine esterase and some lipases. These enzymes appear to hydrolyze their substrates by a mechanism analogous to that of chymotrypsin. Hydrolases such as papain, ficin and bromelain, which are distributed in plants, have a cysteine residue instead of an active serine residue in their active sites. Thus, the transient intermediates are thioesters. 

Its mechanism of action, however, is not completely elucidated. Kamakura et al. [94] studied the effects of stem bromelain on the plasma kallikrein system, bradykinin levels and plasma exudation at the inflammatory site in rats with a kaolin-induced inflammation of an air pouch. Bromelain caused a dose-dependent decrease of bradykinin levels (measured with the method of Minami et al. [95]) at the inflammatory site and a parallel decrease of the prekallikrein levels in sera [88]. Plasma exudation was also reduced dose-dependently. Bradykinin-degrading activity in sera was elevated after bromelain treatment, but not in the pouch fluid. The authors conclude that bromelain inhibits plasma exudation through inhibition of the bradykinin generation at the inflammatory site via depletion of the plasma kallikrein system. Bromelain also shows a dose-dependent analgesic effect in concanavalin A-injected paws of 5.6 mg/kg i.v.), considered to be due to decrease of high molecular weight kininogen [96]. 

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