Study On The Interaction Between Cyclodextrin And Lipoxygenase

Cyclodextrins(CDs) can promote or inhibit the catalytic activity lipoxygenase(LOX)with the formation of CD-LOX complex. LOX catalyzes the oxidation of Linoleic acid(LA)and produces unpleasant odor in many foods. It is reported that CDs have inhibition effects onthe catalytic reaction initiated by LOX. It is believed that probably CDs complexed with LA,resulting in the decrease of LA available, and then the catalytic reaction rate was reduced.However, there is no systematic research on the interaction between CD and LOX from theview of CD-protein supramolecular system. Therefore, the possibility of interaction betweenCD and LOX was discussed with LOX as the subject in this paper. Moreover, the factorsinfluencing interaction between CD and LOX combined with its possible mechanism werestudied. This can serve as fundamental basis for the study of the CD-enzyme supramolecularsystem and the application of CDs in dispelling off-flavor in soybean products.The hypothesis of the existence of interaction between CD and LOX was raised andverified. The results showed that: CDs inhibited the catalytic reaction of LOX. Apart from thedecrease of LA available caused by the forming of CD-LA inclusion, the interaction betweenCDs and LOX also contributed to the inhibition. Compared with the inhibition effects causedby CD-LA inclusion(inhibition rate56.45%), the interaction between CDs and LOX played aleading and dominant role in factors accounting for the inhibition of catalyticreaction(inhibition rate86.26%). These can provide preliminary evidence to support thehypothesis of interaction between CD and LOX.The hypothesis of the interaction between hydrophobic cavities of CDs and LOX wasdemonstrated. Sodium benzoate was added into the interaction system of CD and LOX. Theresults showed that the benzene ring of sodium benzoate instead of LOX had priority tooccupy cavities of CD. Thereby, the probability of LOX interaction with cavities of CDsharply declined with the inhibition rate falling from85.85%to40.31%and the protection onthe activity of LOX was realized. Thus, it can be inferred that it is the hydrophobic cavities ofCD that interacted with specific sites of LOX. Then the CD-LOX complexion formed,resulting in the decrease of catalytic activity of LOX.The factors influencing interaction and kinetic characteristics between CD and LOXwere explored. Effects of different cavity sizes were investigated. The results showed that thecavity size of β-CD performed the best matching effect with specific groups of LOXcompared with α, γ-CD. The interaction between CD and LOX had a concentration-dependenteffect. As the side chain of CD increased, steric hindrance increased and the inhibition effectreduced. The influence of temperature, pH and soybean protein on the interaction between CDand LOX were studied. The results revealed that CD-LOX interaction was not only relatedwith the hydrophobic cavities of CD, but also with the influential factors of LOX itself, suchas temperature and pH. Soybean protein weakened the activity inhibition of LOX by CD. Thenonlinear inhibitory behavior made it a mixed inhibition type. Probably it is not the active siteof LOX that can bind to CD.The mechanism of activity inhibition of LOX by CD was explored. The intrinsic fluorescence and circular dichroism behaviour of LOX in the presence of CD wereinvestigated. The results revealed that fluorescent amino acid residues of LOX were inducedto be exposed and to complex with CDs. The microenvironment of LOX changed, resulting inenzyme conformation alteration. CDs could also bring about considerable variability to thesecondary structure composition and the circular dichroism features of several hydrophobicamino acid residues LOX in the near UV region, resulting in the rearrangement ofzymoprotein and the modification of its spatial structure, and thus, the activity of LOX wasinhibited.