The cytochrome system of the Cecropia silkworm. I. Spectroscopic studies of individual tissues

Abstract

Except in the somatic muscles (which throughout metamorphosis retain a classical cytochrome system in high concentration), the cytochrome system of the Cecropia silkworm is known to undergo marked changes during the course of metamorphosis, especially in relation to the onset and termination of the pupal diapause. These changes have now been studied in individual tissues and organs by the technique of low-temperature spectroscopy. The larval tissues contain a complete cytochrome system including moderate to high concentrations of cytochromes a + a 3 , b , c and b 5 . By contrast, the tissues of the diapausing pupa show a seemingly incomplete cytochrome system in that components b and c are not detectable; cytochromes a + a 3 and b 5 persist in low though still detectable concentration. Consequently, the onset of pupal diapause is accompanied by a generalized decrease in concentration of the several cytochromes, including the virtual disappearance of b and c . Several months later, when the insect’s prothoracic glands function to terminate diapause, cytochromes b and c promptly reappear and, together with a + a 3 and b 5 , then undergo a progressive increase in concentration during adult development. The net result is that the post-diapausing tissues are re-equipped with a normal cytochrome system. In view of the intracellular localization of cytochromes a + a 3 , b and c in mitochondria, and that of b 5 in the endoplasmic reticulum, the results of the present study implicate prominent alterations in these organelles during the course of metamorphosis. And, since the growth and development of the post-diapausing insect are known to require the renewed presence and function of a normal cytochrome system, the resynthesis of this system at the termination of diapause is evidently closely linked to the action of the prothoracic gland hormone.