An analysis of pH tolerance and substrate preference of isolated skeletal muscle mitochondria from Bufo marinus and Rana catesbeiana.

1. The effects of varying pH and substrate on isolated skeletal muscle mitochondria from Bufo marinus and Rana catesbeiana were investigated. 2. For both species, VO2 max significantly decreased at all pH < 7.3 (P < 0.05), while maximum values were observed at a pH range of 7.3-7.6 with B. marinus maintaining a greater VO2 max than R. catesbeiana. 3. Respiratory control values (RCR) decreased significantly at all pH < 6.9 for both species (P < 0.05). 4. Isolated mitochondria from both species were maintained at pH = 7.2 and O2 consumption measured under five separate substrate conditions. 5. A rank preference was established based upon state 3 and RCR values. 6. Substrate preference was identical for both species and interspecific comparisons revealed differences in state 3 respiration and coupling.