Effects of Cyclodextrin Derivatives on the Catalytic Activity of Tyrosine Phenol-Lyase

Bridging of a substrate between cyclodextrin and an enzyme's active site pocket triggers a unique mode of inhibition

“…As concluded by other investigators, we suspected that the presence of HP-β-CD depleted the free substrate (due to the formation of the HP-β-CD-substrate complex) leading to the impairment in the catalytic rate of the enzyme. Such expectation has been in accord with the literature precedent that CD inhibits catalysis of other enzymes by sequestering their substrates and thus reducing the concentration of free substrates in solution [29–31,45]. To probe whether or not the HP-β-CD mediated inhibition of MetAP was exclusively due to the sequestration/depletion of the enzyme’s substrate; we proceeded to determine the binding affinity of MetAMC substrate with HP-β-CD as well as determine the kinetic parameters of the MetAP catalyzed reaction under an identical experimental condition.…”

“…Such variations involved (among others): (i) HP-β-CD— MetAMC complex not being converted to HP-β-CD—MetAMC—MetAP complex as found in the case of the CD dependent inhibition of polyphenol oxidases as well as other enzymes [45,49], (ii) HP-β-CD—MetAMC—MetAP serving as the productive complex, (iii) interaction of HP-β-CD with free enzyme (followed by formation of HP-β-CD—MetAMC—MetAP complex). To analyze the data of Figure 5 by the model of Scheme-3 vis a vis its variants, we employed Dynafit software.…”

“…This could be easily conceived by comparing the experimental rates of enzyme catalysis in the presence of HP-β-CD versus those predicted on the basis of reduction in the free substrate concentration due to sequestration by HP-β-CD (Figure 4A). There are some reports on the non-competitive or mixed inhibition of selected enzymes by cyclodextrins which have been attributed to an unknown mode of cyclodextrin-enzyme interaction in addition to the observed sequestration of substrate [30,45,56,57]. To our surprise (and contrary to the reports of the reversal of inhibition of the enzyme activity by CD in the presence of increasing concentrations of substrate; [58]), we observed that increase in the substrate (MetAMC) concentration enhanced the magnitude of inhibition of the enzyme by HP-β-CD (Figure 4B).…”

The influence of selected O-alkyl derivatives of cyclodextrins on the enzymatic decomposition of l-tryptophan by l-tryptophan indole-lyase

“…5,6 In our previous work, we studied the effect of the addition of permethylated cyclodextrins on the enzymatic reaction of tyrosine phenol-lyase. 7 For both permethylated a-and b-CDs, we have noticed the inhibition of the enzymatic reaction. On the other hand, the permethylated c-CD has caused the activation of tyrosine phenol-lyase.…”

“…2 Therefore, an increased interest in applications of CDs in enzymology has been observed in the past few years. [3][4][5][6][7][8] The CDs are used in enzyme studies as additives 3 (which alter the rate of the enzymatic reactions) and also as covalent modifiers of the enzymes 4 (the modified enzyme was more catalytically active and thermally stable than the native one). Another example of the applications of modified CDs in enzymology has been the co-lyophilization of CDs with the enzymes.…”