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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.
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