Diversity in digestive proteinase activity among insects.

pH-optimum curves for proteolytic activity from midgut homogenates of 23 species of insects were determined using a radiometric proteinase assay. Optima for digestion of radiolabeled methemoglobin in these insects ranged from pH 3.0 to pH 12.0. Since pH optima vary among the different mechanistic classes of proteinases, these data suggest that there is high diversity in midgut digestive proteinases among various insects.