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Pepsin, conformation

AP+ ions, physiological and toxic ones, on pepsin conformational stability during the process of thermal unfolding, with a purpose of better understanding of pepsin/aluminium interaction. [Pg.278]

The mutant porcine pepsins, T77D, G78(S)S79, and T77D/G78(S)S79, were purified by the same method as wild-type pepsin, and the purities of the enzymes were judged by SDS-PAGE. The NH2-terminal sequences of the mutants were the same as that of wild-type enzyme. The secondary structures of recombinant wild-type and mutant pepsins were analyzed by CD spectrometry to determine whether localized or global changes of structures were induced by the mutations. The CD spectral data showed that the spectra of the mutants were essentially superimposable on that of the wild-type enzyme. These results suggest that no major conformational alterations occurred in the mutant enzymes. [Pg.193]

The specificities of the various digestive exo- and endopep-tidases suggest that they act synergistically to fulfill a major nutritional function. The concerted action of trypsin, chy-motrypsin, pepsin, and carboxypeptidases A and B facilitate and ensure formation of essential amino acids. The chemical characteristics and metalloenzyme nature of two bovine exopeptidases, lens aminopeptidase and pancreatic carboxy-peptidase A, indicate similarities in their mechanisms of action. However, the aminopeptidase exhibits an unusual type of metal ion activation not observed unth carboxy-peptidase. Chemical and physicochemical studies reveal that the latter enzyme has different structural conformations in its crystal and solution states. Moreover, various kinetic data indicate that its mode of action toward ester substrates differs from that toward peptide substrates. The active site metal atom of carboxypeptidase figures prominently in these differences. [Pg.220]

The rate of enzyme-catalyzed reactions typically shows a marked dependence on pH (Figure 8-7). Many of the enzymes in blood plasma show maximum activity in vitro in the pH range from 7 to 8. However, activity has been observed at pH values as low as 1.5 (pepsin) and as high as 10.5 (ALP). The optimal pH for a given forward reaction may be different from the optimal pH found for the corresponding reverse reaction. The form of tlie pH-dependence curve is a result of a number of separate effects including the ionization of the substrate and the extent of dissociation of certain key amino acid side chains in the protein molecule, both at the active center and elsewhere in the molecule. Both pH and ionic environment will also have an effect on the three-dimensional conformation of the protein and... [Pg.203]

After a 75-hour HC1 hydrolysis of the native, iron-containing, G. gouldii protein only 5% of the threonine was destroyed while the same treatment on the iron-free species resulted in 37% degradation of this residue (169). A related finding is that nitrated, heat-denatured apo-hemerythrin is hydrolyzed by pepsin faster than acid denatured nitro-hemerythrin (201). Furthermore, carboxypeptidase A, which reacted immediately on the iron-free protein, did not release any amino acid from native methemerythrin even after incubation for 8 hours, suggesting the conformation of the undenatured protein prevents access of the peptidase to the carboxyl terminus residue of the polypeptide chain (169). Of similar implications, but related to the amino terminus, is the earlier observation that pork kidney leucine amino peptidase does not release any amino acid from hemerythrin (206). [Pg.175]

Data is accumulating for pepsin and HIV protease to suggest that they may catalyze their reactions through a mechanism in which release of products leaves the enzyme in a conformation which must undergo isomerization before another round of catalysis can commence [65]. More work is needed here to eliminate other mechanistic possibilities. [Pg.1469]

In contrast, however, we have demonstrated that the macromolecular conformation of the zymogen differs markedly from that of the enzyme (17). Thus, if pepsinogen is transferred from an aqueous solution to concentrated urea, the specific rotation, [a]m, decreases from —200° to —320° in the concentration range of 1.5 to 4.0M urea, and the rotatory dispersion constant, Xc, decreases from 236 to 216 m/z. As shown in Figure 2, which also includes the results obtained with pepsin, this change reflects a configurational transition, similar in sharpness to the transition from an a-... [Pg.277]


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See also in sourсe #XX -- [ Pg.268 ]




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