Darren:
I'm not sure I fully understand both questions, but here is my attempt.....
Most of the energetically relevant NADH is actually produced within the
mitochondria by the citric acid cycle. NADH movement into mitochondria is
generally thought to occur as a result of the malate-aspartate shuttle
system: Oxaloacetate in the cytosol is reduced to malate by NADH. The malate
enters the mitochondria via the malate transporter. Then, within the
mitochondria malate reduces NAD+ to NADH and becomes oxaoloacetate. The
oxaloacetate is recycled back to the cytosol via aspartate. This results in
a net movement of NADH "reducing equivalents" from the cytosol to the
mitochondiral matrix. So, the real question is "how does NAD+ get into the
mitochondria"? I checked the database.....a by one of my competitors (!) is
one of the few straightforward studies on the subject. I pasted in the
abstract at the end of this message.
As to the number of ATPs formed per glucose....the theoretical yield is 38
ATPs. However, ATP is synthesized as a result of the H+ gradiaent
generated by the electron transport chain. So, any other mechanism that
allows H+ movement across the membrane (without ATP synthesis) can decrease
the efficiency. One specific example is the H+/phosphate transporter; this
is necessary to import inorganic phosphate needed to convert ADP to ATP
within the mitochondria. So, in reality the 38 ATP per glucose is rarely
attained.
I hope this helps!
Bob Tallitsch
Hello All.
I'm trying to find some information on the specific types of cells
that use a shuttle mechanism to move NADH into the mitochondria. Also,
if anyone has any suggestions about where to get some more specifics
on this process of why we get 36-38 ATP I would appreciate it.
Thanks! Hope everyone has a great semester!
Darren Mattone
Department of Biology
Muskegon Community College
Muskegon,Mi
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Robert B. Tallitsch, Ph.D.
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