Cysteine proteases ficin

Corresponding equations were derived for the cysteine proteases ficin, actinidin, bromelain B and D, and the serine proteases subtilisin, chymotrypsin, and trypsin. In all cases, the coefficient of the electronic a term is around 0.4-0.7. Whereas the other regression coefficients in equations (16) and (17) are also relatively similar, the constant terms of both equations differ by about 1.8 log units, which indicates that the lower lipophilicity of the mesyl group, as compared with a much more lipophilic benzoyl group, is responsible for the lower binding affinities of the mesyl amides. To prove this hypothesis, a series of (4-X-Phe)-CONHCH2COO-pyrid-3-yl analogs 12 was synthesized and tested. As expected, lipophilicity determines the structure-activity relationship in this part of the molecules (equation IS). " " ... 

Cysteine proteases are so called because of a critical cysteine involved (together with an adjacent histidine) in the catalytic mechanism. Cysteine proteases include papain-related proteases, calpain-related proteases and the caspases. Papain-like cysteine proteases include the plant enzymes actinidin, aleurain, bromelain, caricain, chymopapain, ficin and papain and the lysosomal cathepsins B, C, H, K, L and S. Cathepsin C is multimeric (MW -200,000), but the other papain-related proteases are monomeric with MWs of about 20,000-35,000. While cathepsin C is a dipeptidyl aminopeptidase, the other enzymes are endopeptidases. Cathepsin B is an endopeptidase and a dipeptidyl carboxypeptidase. Cathepsin H is an endopeptidase and an aminopeptidase. In higher animals, cathepsin B generates peptides from antigens for presentation to T cells by the major histocompatibility... 

The reactivity of the Ru-pac complexes toward the binding of the above thio-amino acids (RSH) has been reportedly used to explore the potential role of Ru-pac complexes in the inhibition of the activity of cysteine protease (CP) (25,26) and protein tyrosine phosphatase (PTP) (28). The Ru-pac complexes were found to inhibit protease activity of the three enzymes bromalien, papain, and ficin, while azo-albumine was used as the substrate (25,26). The ability of Ru-pac complexes to inhibit CP activity was attributed to the high affinity of the ruthenium complexes toward binding the SH group in the cysteine residue of the enzymes via a rapid aqua-substitution reaction (Scheme 8). 

In this context, many micellar enzyme analogues of serine proteases have been prepared (131). Cysteine proteases, however, such as papain and ficin, have been modeled only recently (163). 

In enzymes, the most common nucleophilic groups that are functional in catalysis are the serine hydroxyl—which occurs in the serine proteases, cholinesterases, esterases, lipases, and alkaline phosphatases—and the cysteine thiol—which occurs in the thiol proteases (papain, ficin, and bromelain), in glyceraldehyde 3-phosphate dehydrogenase, etc. The imidazole of histidine usually functions as an acid-base catalyst and enhances the nucleophilicity of hydroxyl and thiol groups, but it sometimes acts as a nucleophile with the phos-phoryl group in phosphate transfer (Table 2.5). 

The group of cysteine endopeptidases (also called sulfhydryl proteases or thiol proteases) include the higher plant enzymes papain (EC 3.4.22.2) and ficin (EC 3.4.22.3), but also numerous microbial proteolytic enzymes such as Streptococcus cysteine proteinase (EC 3.4.22.10). The enzymes have a rather broad substrate specificity, and specifically recognise aromatic substituents. The specificity is for the second amino acid from the peptide bond to be cleaved. 

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