The Catalytic Environment and its Biological Implications

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Abstract
This review concerns itself with the author''s theory that the stability, activation, and especially inactivation effects on enzymes may often be induced by environmental factors, particularly by substrates and cofactors; that these effects are often probably related to conformational changes; and that they play a most important role in regulation of enzyme activity and its manifestations in a broad spectrum of biological phenomena. It is probable that substrates either stabilize, have no effect on, or decrease the stability of the enzyme by affecting the active site, particularly if the substrate does not fit precisely the site. Effects on the modifying center may produce the same results. In many cases elasticity and/or plasticity may be involved. Again in all cases, a second substrate, a cofactor, or another reagent may affect the stability or activity by influencing directly or indirectly the active site or the modifier site. On the basis of work done with carbamyl-P synthetase and other enzymes which supports the concept of nontransient deformation, and on the basis that all substrate-induced inactivations thus far studied are irreversible, it appears that plasticity with change in conformation is involved fairly often. Possibly sub-strate-inactivation facilitates the formation of the so-called abortive complexes. Since substrate interaction may either protect an active center, or by changing the geometry of the enzyme make other groups more susceptible to inactivation by physical agents, the author suggests that this phenomenon may play an important role in biology, for example, in enzyme-protein turnover and enzyme life span.