Autoimmune Thyroid Disease

An Unfortunate and Lengthy Adventure in Misdiagnosis

Papain and bromelain

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I think I’ve found the reason, or one of the reasons, why pineapple and papaya could be particularly problematic foods for failsafers.

Papain turns out not to be “an enzyme that helps you to digest protein”, but a cysteine protease!

Papain is a cysteine protease (EC 3.4.22.2) present in papaya (Carica papaya) which is useful in tenderizing meat and other proteins. It consists of 212 amino acids stabilised by 3 disulfide bridges. Its 3D structure consists of 2 distinct structural domains with a cleft between them. This cleft contains the active site, which contains a catalytic triad that has been likened to that of chymotrypsin. Its catalytic triad is made up of 3 amino acids – cysteine-25 (from which it gets its classification), histidine-159, and asparagine-175.

The mechanism by which it breaks peptide bonds involves deprotonation of Cys-25 by His-159. Asn-175 helps to orient the imidazole ring of His-159 to allow this deprotonation to take place. Cys-25 then performs a nucleophilic attack on the carbonyl carbon of a peptide backbone. This frees the amino terminal of the peptide, and forms a covalent acyl-enzyme intermediate. The enzyme is then deacylated by a water molecule, and releases the carboxy terminal portion of the peptide. Papain, Wikipedia

—- snip —-

Proteases are enzymes that degrade polypeptides. Cysteine proteases have a common catalytic mechanism that involves a nucleophilic cysteine thiol in a catalytic triad. The first step is deprotonation of a thiol in the enzyme’s active site by an adjacent amino acid with a basic side chain, usually a histidine residue. The next step is nucleophilic attack by the deprotonated cysteine’s anionic sulfur on the substrate carbonyl carbon. In this step, a fragment of the substrate is released with an amine terminus, the histidine residue in the protease is restored to its deprotonated form, and a thioester intermediate linking the new carboxy-terminus of the substrate to the cysteine thiol is formed. The thioester bond is subsequently hydrolyzed to generate a carboxylic acid moiety on the remaining substrate fragment, while regenerating the free enzyme. Cysteine Protease, Wikipedia

So is bromelain, which is also a sulphur containing protease.

Bromelain is not a single substance, but rather a collection of enzymes and other compounds. It is a mixture of sulfur-containing protein-digesting enzymes—called proteolytic enzymes or proteases—and several other substances in smaller quantities including: peroxidase, acid phosphatase, protease inhibitors, and calcium. Bromelain, Wikipedia

Question: What do you get when you break down sulphur containing proteins? Answer: You get sulphur, sulphides, and sulphites.

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Written by alienrobotgirl

4 September, 2006 at 11:45 am

Posted in The Science of FCI

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