Respiration and phosphorylation by mitochondria from the hepatopancreas of the blue crab (Callinectes sapidus)

Mitochondria isolated from the hepatopancreas of the blue crab Callinectes sapidus show high rates of oxidation of pyruvate + proline and of various intermediates of the tricarboxylic acid cycle in a 280- to 380-mOsm sucrose-mannitol medium supplemented with bovine serum albumin. The respiratory control ratio ranged from 6 to 10. Respiration was accompanied by phosphorylation of ADP, with the expected ADP:O ratio for all substrates tested except α-ketoglutarate, indicating that all three energy-conserving sites were functional. Fatty acids were also oxidized, but no oxidation of β-hydroxybutyrate, glycerol 3-phosphate, or NADH was observed. The crab mitochondria showed a relatively low affinity for phosphate, but a normal affinity for ADP. Respiration and phosphorylation gave the normal responses to respiratory chain inhibitors, uncoupling agents, oligomycin, and ionophores. Crab mitochondria have an exceptionally high content of phosphate, exceeding 1000 nmoles per mg protein, but a normal energy charge of the adenylic system. An unusual feature is the presence of considerable arginine kinase activity, which is usually thought to be restricted to muscle and nerve tissue in anthropods. This enzyme allows arginine to act as secondary phosphate acceptor. The arginine kinase is located on the cytosol side of the atractyloside-sensitive barrier and is thus unable to transfer the terminal phosphate group of matrix ATP directly to arginine.