Papain esterase

Later, oxyanion holes were also discovered in other proteases, such as the cysteine protease papain, and in esterases and lipases, enzymes capable of esterification or ester hydrolysis. Interestingly, in these esterases, sometimes up to three hydrogen bond donors can be located within 3 A of the carbonyl oxygen atom, whereas such triple hydrogen bonding motifs have not yet been found in the proteases. 

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 solubilizing capacity of the choline residue is so pronounced that even substrates combining two hydrophobic amino acids are homogeneously soluble in aqueous buffer without any additional cosolvent. These favorable physical properties were also used in the enzymatic formation of peptide bonds. The amino acid choline ester 38 acts as the carboxyl component in kinetically controlled peptide syntheses with the amino acid amides 39 and 40 [52] (Fig. 11). The fully protected peptides 41 and 42 were built up by means of chymotrypsin in good yields. Other proteases like papain accept choline esters as substrates also, and even butyrylcholine esterase itself is able to generate peptides from these electrophiles. 

However, the closely related amino acid 133 was not a substrate for either lipase (from pigs or Candida) but could be resolved with the proteolytic enzyme papain. This acted as an esterase, hydrolysing the methyl ester rather than the amide. Note that this kinetic resolution produces a single enantiomer of the carboxylic acid rather than the alcohol and that separation of 134 from 133 is very easy as the free acid can be extracted from organic solvents by aqueous base in which it is soluble as the anion. 

The reported applications of esterolytic applications used esterases (21%), lipases (63%), and proteases (16%). The most often and widely used biocatalysts were pig liver esterase, pig pancreatic lipase and lipase from Candida cylindracea. Among the proteases, a-chymotryp-sin, papain, penicillin aminoacylase and subtilisin were used most frequently. In the case of stereospecific reductions of carbonyl compounds the use of whole cells of baker s yeast (Sac-charomyces cerevisiae) [75-77] accounted for 54% of the total dehydrogenase applications. The dominance of just very few biocatalytic systems, seems to indicate the direction in which... 

The second problem is caused by possible decomposition of the other ingredients under effect of TAS. For example, papain has both protease and esterase activity and therefore it can decompose ingredients containing peptide and ester links, for example, surfactants, emollients, thickeners, etc. The third problem is that the solutions of enzymes and other TAS cannot provide a slow-release effect in liquid remedies. 

The mechanism of amide- and ester-hydrolyzing enzymes is very similar to that observed in the chemical hydrolysis by a base. A nucleophilic group from the active site of the enzyme attacks the carbonyl group of the substrate ester or amide. This nucleophilic chemical operator can be either the hydroxy group of a serine (e.g., pig fiver esterase, subtifisin, and the majority of microbial lipases), a carboxyl group of an aspartic acid (e.g., pepsin) [3], or the thiol functionality of cysteine (e.g., papain) [4-6]. 

The thiol enzyme for which the most detailed mechanistic formulations have been proposed is papain . In this enzyme a cysteine thiol group appears to function in the same manner as the serine hydroxyl of other proteases and esterases. In the hydrolysis of proteins by this plant protease there is an intermediate formation of an acyl thiol, which is subsequently cleaved by water. 

Urethane and urea bonds Hydrolysis it can be catalysed by enzymes, such as cholesterol esterase and proteases (papain, bromelain, and ficin) and Protease K and chymotrypsin Relatively slow due to the microphase separation of urethane/urea bonds into PUR hard segments... 

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. 

In addition, in-vitro investigations have found that polyethylene terephthalate is degraded by esterases and papain [978]. 

The three crystalline proteolytic enzymes of pancreas—trypsin, chymotrypsin, and carbox3rpeptidase— possess a well-defined esterase activity on appropriate synthetic compounds which are closely related in structure to substrates possessing amide or peptide bonds (126). Crystalline papain also has an esterase action (99,100). 

Poly(ether-urethane)s have been extensively used in vivo as implants, due to their good blood compatibility, as well as their bioresistance, concluded from earlier studies. However, more recent studies have reported evidence of degradation by many enzymes (papain, bromelain, ficin, chymotrypsin, trypsin, cathepsin C, lysosomal enzymes, and esterase). ... 

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