It is well accepted that papain and cathepsin B work by stabilizing the transition state of the substrate formed during catalysis. This species carries a formal negative charge which, in the serine proteases family, is stabilized by an oxyanion hole formed by the enzyme. The same structure has been proposed to exist for cysteine proteases. Because the side chain of a Gln residue contributes one stabilizing hydrogen bond to the transition state in the oxyanion hole of papain and cathepsin B, site directed mutagenesis was used in this work to change this residue to Ala and Ser. It was found that this Gln contributes between 2.5 and 3.7 kcal/mol to the transition state stabilization in papain and 3.7 kcal/mol for cathepsin B. The pH profile of cathepsin B is also shifted to higher pH indicating a destabilization of the catalytic ion-pair caused by the mutation. These results demonstrate that the oxyanion hole plays an active role in catalysis by cysteine proteases. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.61324 |
| Date | January 1992 |
| Creators | Carrière, Julie |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Biochemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001307222, proquestno: AAIMM80340, Theses scanned by UMI/ProQuest. |
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