Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/2/2005
Publication Date: 2/28/2005
Citation: Oppert, B.S., Morgan, T.D., Hartzer, K.L., Kramer, K.J. 2005. Compensatory proteolytic responses to dietary proteinase inhibitors in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Comparative Biochemistry and Physiology, Part C 140: 53-58. Interpretive Summary: The red flour beetle is a major pest of grains and grain products. Our previous experiments suggested that combinations of digestive enzyme inhibitors could decrease growth and increase mortality of red flour beetle larvae. To understand the mechanism of inhibition, larvae were fed increasing amounts of two different enzyme inhibitors. Biochemical analysis of gut extracts from larvae indicated that inhibitors of serine proteinases had minor effects on the overall gut proteolytic pattern of digestive proteinases when fed to red flour beetle larvae. However, dietary cysteine proteinase inhibitors induced a shift from cysteine to serine proteinase-based digestion. Therefore, the combination of serine and cysteine proteinase inhibitors in the diet of red flour beetle larvae prevents the adaptive response. Inhibitor combinations in cereals have the potential to prevent damage by red flour beetle larvae.
Technical Abstract: Increasing levels of inhibitors that target cysteine and/or serine proteinases were fed to T. castaneum larvae, and the properties of digestive proteinases were compared in vitro. Cysteine proteinases were the major digestive proteinase class in control larvae, and serine proteinase activity was minor. Dietary serine proteinase inhibitors had minimal effects on either the developmental time or proteolytic activity of T. castaneum larvae. However, when larvae ingested cysteine proteinase inhibitors, there was a dramatic shift from primarily cysteine proteinases to serine proteinases in the proteinase profile of the midgut. Moreover, a combination of cysteine and serine proteinase inhibitors in the diet prevented this shift from cysteine proteinase-based digestion to serine proteinase-based digestion, and there was a corresponding substantial retardation in growth. These data suggest that the synergistic inhibitory effect of a combination of cysteine and serine proteinase inhibitors in the diet of T. castaneum larvae on midgut proteolytic activity and beetle developmental time is achieved through the prevention of the adaptive proteolytic response to overcome the activity of either type of inhibitor.