Variations in the amounts and distribution of the nicotinamide coenzymes during the life cycle of the blowfly Lucilia cuprina have been investigated. 2. The concentrations of NAD and NADP declined to a minimum in mid-pupal life, then increased threefold from this to about 600 and 40mmumoles/g. fresh wt. respectively in the adult. 3. The NADH/NAD ratio was relatively constant (0.15) except in mid-pupal life (0.09); the NADPH/NADP ratio was lower (0.6) in larvae and mated adults than at other stages (0.90). 4. The increase in NAD content during development was greatest in the thorax, which finally contained about 75% of the total coenzyme. 5. Incorporation of NAD into the thoracic sarcosomes began about 2 days before ecdysis. Initially, most (77%) of the coenzyme was in particles 0.2-1mu in diameter, at a concentration of 11.1mmumoles/mg. of protein. During development there was a gradual appearance of NAD in larger particles (1-10mu) containing 2.8mmumoles/mg. of protein. 6. Similar but less marked changes occurred with NADP, which had a final concentration in the large particles of 0.01mmumole/mg. of protein.
