Aspects of the development of flight-muscle sarcosomes in the sheep blowfly, Lucilia cuprina, in relation to changes in the distribution of protein and some respiratory enzymes during metamorphosis.

1. Changes in the amounts and distribution of protein and respiratory enzymes have been estimated during the life cycle of the fly Lucilia cuprina. 2. The fully fed larva contains about 7mg. of protein, the pupa and newly emerged fly about 4mg., and the mature adult about 3mg. 3. There are two periods of incorporation of protein into particles at the expense of the soluble protein; the first, immediately after pupation, may store protein (0.5mg./insect) for use in adult development; the second, over the period of emergence, was due mainly to the development of the thoracic mitochondria of the adult (0.7mg./insect). 4. In the thorax, cytochrome c oxidase and the dehydrogenases for glycerophosphate, isocitrate (NAD-dependent), succinate and malate appeared initially in small particles (less than 1mu in diameter). 5. In adult development these enzymes were redistributed so that in the mature fly most of the activity was present in larger particles (1-10mu in diameter). 6. During this redistribution the specific activity (mul. of oxygen/hr./mg. of protein) of glycerophosphate dehydrogenase in the small particles was 690 at 1(1/2) days before emergence, 955 at emergence and 980 at 7 days after emergence; the corresponding values for the large particles were 164, 760 and 1220. 7. In the mature fly the highest specific activities (mul. of oxygen/hr./mg. of protein) estimated were: glycerophosphate dehydrogenase 1380, isocitrate dehydrogenase (NAD-dependent and requiring ADP and Mg(2+)) 408, succinate dehydrogenase 122, malate dehydrogenase 190, and cytochrome c oxidase 1360. 8. The results are considered in relation to the development of the flight-muscle sarcosomes.