POTENTIAL INFLUENCE OF MIDGUT PH AND REDOX POTENTIAL ON PROTEIN-UTILIZATION IN INSECT HERBIVORES

Early insect physiologists recognized the importance of gut physicoche mistry, primarily pH, redox potential, and ionic strength, on digestiv e processes, but studies to date have been primarily restricted to ker atin- and wood-feeding insects. Recent investigations show that herbiv orous insects have a broad range of gut redox conditions, with pHs ran ging from 6.0 to 11.8 and measured redox potentials from -200 to +240 mV. The redox state of the gut is largely dependent on pH, which is we ll regulated, and the redox activity of ingested material, including p lant chemicals, at that pH. Inter- and intraspecific variation in midg ut redox conditions appears to be substantial enough to affect digesti on via effects on the structure and function of dietary proteins and p roteolytic enzymes. The impact of reducing conditions on proteins prob ably depends on characteristics such as tertiary structure and the num ber and arrangement of disulfide linkages. In addition to the effects of reducing conditions in dietary proteins, there can be effects on th e activities of digestive enzymes, depending on their structure and th e nature of their catalytic site. We speculate that phylogenetic and e nvironmental determinants of gut physicochemistry may place constraint s on the efficacy of different digestive processes, and may thus influ ence the evolution of digestive strategies in insects. (C) 1996 Wiley- Liss, Inc.