The Excretion of Nitrogen in Insects

Abstract

The role of urea in nitrogenous excretion has never been fully understood; it is present in the excreta of many insects, however usually forms a rather minor component. On this basis the insect was assessed as being predominantly uricotelic in a general classification of excretory metabolism. Uricotelism was seen as an adaptation to a terrestrial mode of life; the excretion of toxic end products, like ammonia, or of soluble end products, like urea, was seen as being militated against by the shortage of water. Accumulated data suggests that nitrogenous end products other than uric acid may figure largely in the excreta of a variety of insects; the exceptions are becoming more numerous, and the validity of the earlier generalization appears to be threatened. This chapter discusses the available information, and, in this way, provides some basis for a reassessment of the situation. A number of uricolytic enzymes have been investigated in tissue homogenates, their distribution among different tissues has been established and some of their properties have been described. A great deal has been discovered about xanthine oxidase, or xanthine dehydrogenase as it should more properly be called, and here studies have advanced to the stage of enzyme purification.