Effect of specificity on ligand conformation in acyl-chymotrypsins
| Autor: | Christopher W. Wharton, S S Johal, Andrew J. White |
|---|---|
| Rok vydání: | 1994 |
| Předmět: |
Flexibility (anatomy)
Spectrophotometry Infrared Stereochemistry Acylation Population Resonance Raman spectroscopy Reaction intermediate Ligands Biochemistry Substrate Specificity symbols.namesake medicine Chymotrypsin education Spectroscopy Molecular Biology education.field_of_study Binding Sites Molecular Structure Chemistry Cell Biology Hydrogen-Ion Concentration Ligand (biochemistry) Resonance (chemistry) medicine.anatomical_structure symbols Raman spectroscopy Research Article |
| Zdroj: | Biochemical Journal. 297:281-287 |
| ISSN: | 1470-8728 0264-6021 |
| Popis: | I.r. difference spectroscopy combined with 13C and 18O double-isotope substitution was used to examine the ester acyl carbonyl stretching vibration of hydrocinnamoyl-chymotrypsin. A single acyl carbonyl stretching band was observed at 1731 cm-1. This contrasts with previous i.r. and resonance Raman spectroscopic studies of a number of trans-3-arylacryloyl-chymotrypsins which showed two acyl carbonyl stretching bands in the region of 1700 cm-1, which were proposed to represent productive and non-productive conformations of the acyl-enzyme. The single acyl carbonyl band for hydrocinnamoyl-chymotrypsin suggests only a single conformation, and the comparatively high frequency of this band implies little or no hydrogen-bonding to this carbonyl group. Enzymic hydrogen-bonding to the acyl carbonyl is believed to give bond polarization and thereby catalytic-rate acceleration. Thus, in view of the apparent lack of such hydrogen-bonding in hydrocinnamoyl-chymotrypsin, it should be the case that this acyl-chymotrypsin is less specific than trans-3-arylacryloyl-chymotrypsins, whereas the opposite is true. It is therefore proposed that there may be a productive acyl carbonyl population of lower stretching frequency for hydrocinnamoyl-chymotrypsin, but that this is too small to be discerned because of either a relatively high deacylation rate or an unfavourable conformational equilibrium. The single acyl carbonyl band for hydrocinnamoyl-chymotrypsin is significantly broader than those for trans-3-arylacryloyl-chymotrypsins, indicating that this group is more conformationally mobile and dispersed in the former. This can be correlated with the absence of acyl carbonyl hydrogen-bonding in hydrocinnamoyl-chymotrypsin, and with the much greater flexibility of the saturated hydrocinnamoyl group than unsaturated trans-3-arylacryloyl. This flexibility is presumably the reason why hydrocinnamoyl-chymotrypsin is more specific than trans-3-arylacryloyl-chymotrypsins. Resonance Raman spectroscopy is limited to the non-specific trans-3-arylacryloyl-chymotrypsins because of its chromophoric requirement, whereas i.r. may be used to examine non-chromophoric more specific acyl-enzymes such as hydrocinnamoyl-chymotrypsin. The results presented in this paper suggest that trans-3-arylacryloyl-chymotrypsins are atypical. |
| Databáze: | OpenAIRE |
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