Bioenergetics of mitochondria from flight muscles of aging blowflies: partial reactions of oxidation and phosphorylation.

Mitochondria from flight muscles of senescent blowflies, Phormia regina, which exhibit decreased rates of coupled, or ADP-stimulated, oxidation of α-glycerolphosphate or pyruvate show similar decreased rates of uncoupled, or carbonylcyanide-p-trifluoromethoxyphenylhydrazone-stimulated oxidation. Thus, uncoupled α-glycerolphosphate oxidation is decreased by 20% and uncoupled pyruvate oxidation by 39% in mitochondria isolated from 31- to 33-day-old blowflies as compared with mitochondria from 7- to 9-day-old flies. The finding of nearly equal decreases with age in coupled and uncoupled respiration suggests that the age-dependent defect lies within the oxidative or electron transport pathway, and not associated with phosphorylation. However, no such change with age is observed in any of the partial reactions of electron transport that were examined. These include the following partial reactions: (a) pyruvic dehydrogenase; (b) pyruvate-ferricyanide reductase: (c) α-glycerolphosphate dehydrogenase; (d) α-glycerolphosphate-ferricyanide reductase; and (e) cytochrome oxidase. In addition, no age-associated decline is observed in the content of cytochromes b, c + c₁, a, or a₃ or in the specific activity of the fully activated mitochondrial ATPase (assayed in the presence of carbonylcyanide-p-trifluoromethoxyphenylhydrazone). However, the specific activity of the masked ATPase (assayed in the absence of uncoupler) is increased 38% in mitochondria from senescent blowflies.