The spectrophotometric dissection of the electron transfer system of mitochondria isolated from the hepatopancreas of Carcinus maenas

1. 1. The effect of amytal and antimycin A on the respiratory activity of crab mitochondria has been studied using Warburg respirometers. 2. 2. Concentrations of amytal greater than 4 mM inhibit 94 per cent of the oxygen uptake by the crab mitochondria respiring in fumarate media. In addition, concentrations of amytal greater than 6 mM inhibit 58 per cent of the respiratory activity of the crab mitochondria in succinate media. 3. 3. Concentrations of antimycin A greater than 0·04 μmole/g of mitochondrial protein inhibit 96 per cent of the respiratory activity of the crab mitochondria. The concentration of antimycin A-sensitive site in the crab mitochondria is lower than that of any other electron transfer component. However, it is probably not the rate-limiting factor in the crab respiratory chain. 4. 4. Using specific inhibitors of respiration, difference spectra of the following components in the crab mitochondria have been obtained: 4.1. (a) Nicotinamide adenine dinucleotides. 4.2. (b) Flavoproteins + cytochrome b. 4.3. (c) Cytochromes c + c 1 + a. 4.4. (d) Cytochrome a 3. Hence the presence of NAN, FP and cytochromes b, c, a and a 3 within the crab mitochondria has been confirmed. 5. 5. The sequence in the crab electron transfer system of the following components has been established as being similar to that in other well-characterized mitochondria: NAN, FP, cytochromes b, c, c 1 a and a 3,amytal-sensitive site, antimycin A-sensitive site and cyanide-sensitive site.