Fig. 1. Oxygen consumption in vitro by thoracic homogenate from a 1.11 g Eulaema bombiformis. 50 µl samples were injected into 1.60 ml of assay medium. 20 µl of 40 mmol l^-1 ADP was injected where indicated. No stimulation of respiration by ADP is observed when substrates provided are 0.03 mmol l^-1 palmitoyl L-carnitine + 6 mmol l^-1 proline. Injection of ADP results in stimulation of respiration when 6 mmol l^-1 pyruvate + 6 mmol l^-1 proline are provided as substrates. The slope of the linear part of the trace after ADP injection yields a rate of 144 nanoatoms O min^-1. Note the break at the end of the ADP-stimulated (state 3) rate and the beginning of a lower (state 4) rate, as would normally be expected after depletion of ADP. Because our protocol makes use of crude homogenates, the state 4 rate is still high relative to the state 4 rates obtainable with isolated, well-coupled, mitochondria. In addition, such transitions between state 3 and state 4 rates were not always observed. This is to be expected, given the high contaminating ATPase activities found in tissue homogenates. This limitation in our protocol precluded meaningful estimates of respiratory control (state 3/state 4) and ADP/O ratios.