A classical enzyme active center motif lacks catalytic competence until modulated electrostatically.

@article{Pinitglang1997ACE,
  title={A classical enzyme active center motif lacks catalytic competence until modulated electrostatically.},
  author={Surapong Pinitglang and Aaron Watts and M. Patel and James D. Reid and Michael A. Noble and Sheraz Gul and A Bokth and Ahmed Muhammad Naeem and H Patel and Emrys W. Thomas and Sreejesh Sreedharan and Chandra S Verma and Keith Brocklehurst},
  journal={Biochemistry},
  year={1997},
  volume={36 33},
  pages={
          9968-82
        }
}
The cysteine proteinase superfamily is a source of natural structural variants of value in the investigation of mechanism. It has long been considered axiomatic that catalytic competence of these enzymes mirrors the generation of the ubiquitous catalytic site imidazolium-thiolate ion pair. We here report definitive evidence from kinetic studies supported by electrostatic potential calculations, however, that at least for some of these enzymes the ion pair state which provides the nucleophilic… 
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