Questions about an Electron Transport Chain experiment THX!!!

Rainie rainie_yingying at
Tue Apr 22 23:57:29 EST 2003


To determine which segments of the electron transport system (ETS) are
responsible for proton pumping and hence for ATP synthesis, some
isolated mitochondria with b-hydroxybutyrate, oxidized cytochrome c,
ADP, Pi, and cyanide had been incubated. (Mitochondria have a
NAD+-dependent dehydrogenase that is capable of oxidizing
b-hydroxybutyrate to b-ketobutyrate.)
l	I wonder what the most likely pathway of electron transport in this
system was.
Then, was the electron donor in this system b-hydroxybutyrate 
(since b-hydroxybutyrate + NAD+ ¨¤ NADH + b-ketobutyrate)?

l	As I see cyanide was the only reagent added to the system that is
not a part of the balanced equation for the reaction. Is the purpose
of adding cyanide to the system was to inhibit cytochrome c oxidase,
and thus blocking all electron transport?
         What would the result be if the cyanide had not been added?

l	Would the enzymes of the TCA cycle to be inactivated in this assay
system ?
l	If so is it because of:  the electron transport chain is blocked,
the NADHs produced by the TCA cycle will be accumulated and cannot be
regenerated back to NAD+ within the mitochondria matrix. Since some
key steps require NAD+ as coenzymes, the affected enzyme is not
functioning well without the presence of oxidized form of the
co-enzyme ?

l	Lastly, why is it important that b-hydroxybutyrate cannot be further
metabolized in this system? Lactate is quite similar in structure to
b-hydroxybutyrate but can be metabolized to pyruvate. What effect
would it have had if the investigators had used lactate as the
oxidizable substrate instead of b-hydroxybutyrate?

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