We herein report a density functional theory study of the rate-limiting hydrogen abstraction reaction from the C11 position of linoleic acid (here modeled by means of a (Z,Z)-2,5-heptadiene), by an Fe(III)-OH- of soybean lipoxygenase-1 enzyme. Two active site models of the first coordination sphere of the active site were used. In the small model, we have represented histidines by ammonia, isoleucine by a formic anion, and asparagine by a formamide, whereas in the large model, we used imidazole rings to replace the histidines. No significant electronic differences between the two models were found. However, in the large model an important steric hindrance exists in the entrance channel of the substrate as it approaches the oxygen atom attached to the iron. A Gibbs free energy barrier as high as 20.8 kcal/mol at room temperature was in this case obtained for the hydrogen abstraction. However, the analysis of the factors which determine that value permits the prediction of a notoriously smaller barrier in the complete enzyme.
|Journal||Journal of Physical Chemistry B|
|Publication status||Published - 9 Sep 2004|