The influence of mitochondrial concentration and storage on the respiratory control of isolated plant mitochondria.

The respiration of mitochondria isolated from various plant tissues was studied over a range of mitochondrial concentrations and at various times after isolation. Respiration at 25 C expressed as nanomoles of O(2) per minute per milligram of protein was constant for mitochondrial concentrations higher than some critical amount, usually 0.25 to 1.0 milligram of protein per reaction. Below this concentration the state 3 respiration rate declined and the mitochondria appeared to lose respiratory control. The respiration of isolated mitochondria stored in ice but measured at 25 C generally declined over long time periods although mitochondria from some tissues showed an initial increase. The results indicate that valid comparisons of the respiratory activity of mitochondria isolated from different tissues or from different parts of the same tissue cannot be made at least until the influence of the above factors has been evaluated.