ASCORBATE OXIDATION REDUCTION IN HELICOVERPA-ZEA AS A SCAVENGING SYSTEM AGAINST DIETARY OXIDANTS

We provide evidence of an important role for ascorbate free radical (AFR) reductase, dehydroascorbate (DHA) reductase, glutathione, and glutathione reductase as components of an oxidant-scavenging system in the midgut of larval Helicoverpa zea. Also, midgut ortho-quinone reductase is a potentially important constituent of the protective system against quinones. The midgut activities of AFR reductase, DHA reductase, glutathione reductase, and orthoquinone reductase were, respectively, 168, 22.1, 6, and 39.5 nmol/min/mg protein. The relatively high activity of these enzymes in the midgut provides circumstantial evidence for a protective mechanism utilizing ascorbate as an antioxidant and glutathione and/or NADPH as reductants. To our knowledge, the enzymes AFR reductase and DHA reductase have not been reported in insects. The particular relevance of this system to antioxidant protection, and in particular to the detoxication of quinones formed in damaged leaf tissues, is discussed.