THE IMPETUS for understanding how enzymes function is inspired by their enormous catalytic efficiency and their exquisite substrate stereospecificity. With the advent of the determination of enzyme structure and the application of physical organic tools to examine the reaction coordinate for the enzymatic transformation of the substrate, penetrating insights have been gained as to the number and magnitude of the kinetic steps in the catalytic cycle, the chemical nature of intermediates, and the function of the active site residues contributed by the enzyme. This noninclusive article describes a small number of enzyme-catalyzed reactions from the viewpoint of protein structure, reaction kinetics, and probable chemical identity of intermediates along the reaction pathway. It concludes with our musings as to the chemical origins of the unusual catalytic properties of enzymes.
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