Inhibition of snowshoe hare succinate dehydrogenase activity as a mechanism of deterrence for papyriferic acid in birch

Abstract

The plant secondary metabolite papyriferic acid (PA) deters browsing by snowshoe hares (Lepus americanus) on the juvenile developmental stage of the Alaska paper birch (Betula neoalaskana). However, the physiological mechanism that reduces browsing remains unknown. We used pharmacological assays and molecular modeling to test the hypothesis that inhibition of succinate dehydrogenase (SOH) is a mode of action (MOA) of toxicity of PA in snowshoe hares. We tested this hypothesis by measuring the effect of PA on the activity of SOH in liver mitochondria isolated from wild hares. In addition, we used molecular modeling to determine the specific binding site of PA on SOH. We found that PA inhibits SOH from hares by an uncompetitive mechanism in a dose-dependent manner. Molecular modeling suggests that inhibition of SOH is a result of binding of PA at the ubiquinone binding sites in complex II. Our results provide a MOA for toxicity that may be responsible for the concentration-dependent anti-feedant effects of PA. We propose that snowshoe hares reduce the dose-dependent toxic consequences of PA by relying on efflux transporters and metabolizing enzymes that lower systemic exposure to dietary PA.

Citation

Forbey, Jennifer Sorensen; Pu, Xinzhu; Xu, Dong; Kielland, Knut; Bryant, John. 2011. Inhibition of snowshoe hare succinate dehydrogenase activity as a mechanism of deterrence for papyriferic acid in birch. Journal of Chemical Ecology. 37(12): 1285-1293.