Observations on the Hydrogen‐Activating Enzymes Present during the Metamorphosis of Insects

Abstract

Summary. The aim of this investigation has been t o study the variation of the intermediate oxidative metabolism during insect metab‐olism as reflected in the activity of the dehydrogenase systems. Pupae and praepupoe of %he fly Calliphora erythrocephala Meig, were used and proved to be excellent experimental material for this purpose. The gas metabolism, oxygen consumption, and carbondioxide production, determined by means of the Thunberg‐microspirometer, described a U‐shaped curve during metamor‐phosis. It was shown by the application of Thunbergs' methylene blue method that the experimental animals were carriers of hydro‐gen‐activating enzyme systems. Variations in the hydrogen‐activating capacity of the dehydrogenase systems or their spon‐taneous activity are likewise U‐shaped and of the same order of magnitude as that of the gas metabolism. For this reason i t is assumed that the U‐shaped course of the respiration is, t o a cer‐tain degree, connected with variations in the activity of the de‐hydrogenase systems. There is, however, no absolute agreement between the variations in the gas metabolism and the dehydro‐genase activity. Variations in pH in the serum also give a U‐shaped curve. About 30 organic compounds have been found capable of in‐creasing the hydrogen‐activating capacity of the experimental animals in vitro. There is reason to assume that corresponding dehydrogenases are active during metamorphosis. Also inhibiting substances are observed. Changes in the hydrogen‐activating capacity due t o the ef‐fect of 16 different substances have been followed during the entire metamorphosis. The results obtained show systematic, periodically occurring variations in activity, which are considered an indication of the change in the potential activity of the respec‐tive dehydrogenase systems. The fluctuations in the potential activity seem to occur at definite time intervals and for this reason it is thought that they represent generally critical periods in the intermediary oxidative metabolism during metamorphosis. The changes in the activity of the succino dehydrogenase has been studied during the entire metamorphosis, as well as the inhibitory effect of malonate and the influence of succinate on the spontaneous activity during the same period. The results obtained give reason to assume the existence of a “succinic cycle” during the period of minimal metabolism during the metamorphosis.