Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The proteolytic specificities of chymopapain and papaya proteinase omega were investigated by using the alpha-chains of manatee and mole haemoglobin, whose primary structures are known, as substrates. The resulting peptides from each enzymatic cleavage were isolated by gel filtration on Sephadex G-25, followed by reversed-phase HPLC of the separated peaks and, in some cases, further purified by preparative thin-layer electrophoresis. The purified peptides were then identified on the basis of their amino-acid composition. The proteolytic specificities of chymopapain and papaya proteinase omega, deduced from the experimental cleavage patterns, are compared to that of papain. As in the case of papain, the specificity-determining factor is the amino-acid residue of the substrate that will be bound in subsite S2 (the next but one from the scissible bond). Aromatic residues in this position, preferred by papain, are not important for chymopapain and papaya proteinase omega. Cleavages preferentially occur when S2 is occupied by leucine, valine or threonine. For chymopapain, proline in position S2 also causes cleavage.
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PMID:The thiol proteinases from the latex of Carica papaya L. IV. Proteolytic specificities of chymopapain and papaya proteinase omega determined by digestion of alpha-globin chains. 268

Chymopapain, a cysteine protease of papaya latex, has been purified with the use of fast protein liquid chromatography. Two homogeneous fractions were analyzed for thiol content and thiol reactivity. It was found that peak 1 and peak 2 contained two and three thiol groups, respectively, per mole of enzyme. This result is inconsistent with the general belief that chymopapain contains one essential and one nonessential thiol group and suggests that a significant portion of the thiol groups was oxidized in the previous preparations. Such an oxidation can account for some of the inconsistent results reported in the literature. An irreversibly oxidized nonessential thiol group may modify the catalytic function of chymopapain especially if it is close to the active site. That one thiol group resides indeed in the vicinity of the essential thiol group is clearly demonstrated by the biphasic reactions of chymopapain with disulfide compounds such as 2,2'-dipyridyl disulfide and 5,5'-dithiobis(2-nitrobenzoate). In the first step of these reactions a mixed disulfide is formed between the enzyme and the reactant, which is followed by a first-order, intramolecular reaction leading to the liberation of the second half of the disulfide compound. Furthermore, on addition of one Hg2+ ion, 2 mol of thiol group, one essential and one nonessential, disappears concomitantly. Formation of a disulfide bond between the catalytically competent thiol group and another free thiol group of chymopapain under physiological conditions may be of regulatory importance.
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PMID:Disulfide bond formation between the active-site thiol and one of the several free thiol groups of chymopapain. 380

The X-ray structure of chymopapain, a cysteine proteinase isolated from the latex of the fruits of Carica papaya L., has been determined by molecular replacement methods and refined to a conventional R factor of 0.19 for all observed reflections in the range from 9.5 to 1.7 A resolution. The crystals used in this study contained a unique molecular species of chymopapain with two moles of thiomethyl attached to the two free cysteines per mole of enzyme. A comparison is made with the other known papaya proteinase X-ray structures: papain, caricain, and glycyl endopeptidase. Their backbone conformations are extremely similar except for two loop regions. Both regions are located at the surface of the protein and far away of the active site cleft. In each X-ray structure the same water network was found at the interface between the two domains of the enzyme. A close examination of the active site groove showed that the specificity restrictions dictated by the S2 subsite did not differ significantly among the four proteinases.
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PMID:Structure of chymopapain at 1.7 A resolution. 897 3