The @A00051@ of a chemical @T06446@ at one site of a @M03986@ through the involvement of another @F02555@ in the same molecular entity, without that group appearing to have undergone change in the reaction product. The use of the term should be restricted to cases for which analogous @I03098@ @C00874@ by @CT01038@ bearing that catalytic group is observable. @I03130@ @C00874@ can be detected and expressed in quantitative form by a comparison of the reaction rate with that of a comparable model compound in which the catalytic group is absent, or by measurement of the @E01896@ of the catalytic group.