Competitive Inhibition of Pepsin by Carboxylic Acids
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概要
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In order to obtain evidence for Tang's hypothesis that pepsin (EC 3.4.4.1) forms a hydrophobic bond with the nonpolar side chain or its substrates, the inhibitory effect of carboxylic acids (from formic acid to isobutyric acid) on the activity of pepsin to the synthetic dipeptide, <I>N</I>-carbobenzoxy-L-glutamyl-L-tyrosine, was studied. Kinetic study showed that the inhibition by carboxylic acids was of competitive type. The inhibitor constant <I>K<SUB>i</SUB></I> decreased with an increase in the size of the inhibitor molecule. The free energy change of formation of complex between pepsin and hydrocarbon chain of carboxylic acid, −<I>ΔF</I><SUB>HC</SUB>, increased linearly with the increase in the number of carbon atoms in the hydrocarbon chain of the inhibitor. It was suggested that the hydrophobic interaction between the side chain of amino acid residues in the binding region of the active center of pepsin and the hydrocarbon side chain of the inhibitor was the cause of the inhibition.
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