Monoterpenes as inhibitors of digestive enzymes an

Authors: Kevin D Kohl Elizabeth Pitman Brecken C Robb John W Connelly M Denise Dearing Jennifer Sorensen Forbey

Publish Date: 2015/02/05

Volume: 185, Issue: 4, Pages: 425-434

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Abstract

Many plants produce plant secondary metabolites PSM that inhibit digestive enzymes of herbivores thus limiting nutrient availability In response some specialist herbivores have evolved digestive enzymes that are resistant to inhibition Monoterpenes a class of PSMs have not been investigated with respect to the interference of specific digestive enzymes nor have such interactions been studied in avian herbivores We investigated this interaction in the Greater SageGrouse Phasianidae Centrocercus urophasianus which specializes on monoterpenerich sagebrush species Artemisia spp We first measured the monoterpene concentrations in gut contents of freeranging sagegrouse Next we compared the ability of seven individual monoterpenes present in sagebrush to inhibit a proteindigesting enzyme aminopeptidaseN We also measured the inhibitory effects of PSM extracts from two sagebrush species Inhibition of aminopeptidaseN in sagegrouse was compared to inhibition in chickens Gallus gallus We predicted that sagegrouse enzymes would retain higher activity when incubated with isolated monoterpenes or sagebrush extracts than chicken enzymes We detected unchanged monoterpenes in the gut contents of freeranging sagegrouse We found that three isolated oxygenated monoterpenes borneol camphor and 18cineole inhibited digestive enzymes of both bird species Camphor and 18cineole inhibited enzymes from chickens more than from sagegrouse Extracts from both species of sagebrush had similar inhibition of chicken enzymes but did not inhibit sagegrouse enzymes These results suggest that specific monoterpenes may limit the protein digestibility of plant material by avian herbivores Further this work presents additional evidence that adaptations of digestive enzymes to plant defensive compounds may be a trait of specialist herbivoresWe would like to thank Dr William Karasov Dr Mark Cook and Taylor Jarmes for assistance with obtaining tissues from chickens We also thank S Vasilchenko N Wiggins falconers T Maechtle D Skinner and H Quade as well as Gus the German shorthaired pointer Jack and Kenna the English setters Grace and Bob the gyrfalcons and Gabriel the gyrfalcon/peregrine falcon hybrid for assistance with collecting tissues in the field This research was funded by the Idaho Department of Fish and Game Idaho Governor’s Office for Species Conservation to J S F a University of Utah Undergraduate Research Opportunities Grant to E P the National Science Foundation DEB1146194 and IOS1258217 to J S F DEB1210094 to M D D and K D K and DBI1400456 to K D K and Idaho INBRE ProgramNIH Grant P20 GM103408 to JSF This is a contribution from Idaho Federal Aid in Wildlife Restoration Project W160R

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