title: A two-binding-site kinetic model for the ribonuclease-T1-catalysed transesterification of dinucleoside phosphate substrates.
abstract: Ribonucleases have been found to have subsites that confer large rate enhancements but do not contribute to substrate binding. In this study, we present a kinetic model that formally explains how subsite binding energy is converted into chemical activation energy. The proposed mechanism takes into account a primary specificity site and a subsite, both of which must be occupied for chemical turnover. An unstable reaction intermediate is formed upon binding of the polymeric substrate monomers at the corresponding subsites. The structure of this reaction intermediate resembles the transition state of the catalysed transphosphorylation reaction. Similar mechanisms may be used by other depolymerizing enzymes including nucleases, glycosidases, and proteases.
authors.affiliation: Laboratory of Ultrastructure, Vlaams Interuniversitair Instituut Biothechnologie, Vrije Universiteit Brussel, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Steyaert
authors.forename: Y
authors.initials: Y
authors.lastname: Engelborghs
mesh_terms: D001665:Binding Sites; D015226:Dinucleoside Phosphates; D004951:Esterification; D007700:Kinetics; D008954:Models, Biological; D006163:Ribonuclease T1 / Q000378:metabolism*; D013379:Substrate Specificity; D013816:Thermodynamics
chemical_list: D015226:Dinucleoside Phosphates; D006163:Ribonuclease T1