Figure 4.

A, Determination of PUMP-sustained respiration. Mitochondria (mito) were incubated in a standard reaction medium in the presence of 2.5 μg oligomycin mg⁻¹ protein and 2 mm BHAM, as described in Methods; 10 μm LA, 0.5% BSA, 1 mm GTP, and 1 μm FCCP were added. The numbers on the traces refer to the O₂-consumption rates in nmol min⁻¹ mg⁻¹ protein. The numbers in parentheses refer to the slopes used to calculate the total PUMP activity and stimulation by LA shown in B. The respiration of green tomato mitochondria is shown as an example. B, PUMP-sustained respiration in the four stages of ripeness (G, green; Y, yellow; O, orange; and R, red). ▪, Total PUMP activity plus H⁺ leak (respiration after the addition of LA; slope 2 from A); ▴, endogenous PUMP activity plus H⁺ leak in the absence of LA (respiration before the addition of LA; slope 1 from A); •, H⁺ leak (respiration after the addition of BSA and GTP; slope 3 from A). Respiratory rates are in nmol O₂ min⁻¹ mg⁻¹ protein. The data are presented as the means ± sd from three to four independent experiments.