Alkaline proteases from the gut fluids of detritus-feeding larvae of the crane fly, Tipula abdominalis (say) (diptera, tipulidae)

Abstract

The high level of proteolytic activity present in the midgut fluids of the detritus-feeding larvae of the crane fly, Tipula abdominalis, is due to a mixture of enzymes, consisting largely of serine proteases with trypsin- or chymotrypsin-like substrate specificities. These enzymes have high alkaline pH optima ( pH > 11 ) and high stability at pH values of 8.5–11.5 at 15°C, properties that enable them to function effectively in the highly alkaline gut fluids (pH 9.5–11.5) of an insect that feeds and grows in cold water (0–25°C). The enzymes also have very low isoelectric points (pH < 6), resulting in their having a high negative charge in vivo. Possibly their anionic character prevents their inactivation through adsorption on ingested lignin, humic acid or clay. These serine enzymes arise from the midgut epithelial cells, and not from microbes residing in the gut or from ingested detrital food. The digestive system of T. abdominalis larvae is adapted for the efficient utilization of the limited quantities of dietary protein present in detrital food.