SDH activity in cauliflower mitochondria.

[tcrosby]

In a cell biology lab we tested the rate of SDH activity in cauliflower mitochondria. We did this by mechanical disruption and centrifugation. We obtained a mitochondria fraction as well as a mitochondria-free fraction. We then blocked the electron transport with the poison sodium azide. We then added a dye, DCIP, that acted as an electron acceptor. We measured the color change in the dye with a spectrophotometer as it accepted electrons and used these values as an indirect measure of SDH activity. The mitochondria fractioned showed a lot of SDH activity while the mitochondria-free fraction showed a little.

 

My question is where were the free electrons coming from in the mitochondria-free fraction? Clearly, the centrifugation may not have been perfect leaving some mitochondria in the mitochondria-free fraction. But I need to come up with a biological reason why this would occur. Any help would be greatly appreciated.

T Crosby