CLINICAL CASES
251
[27.3]
If the patient described does indeed have angina, his is a focal lesion
wherein only one portion of heart muscle is affected while other por-
tions still receive adequate oxygen enabling the malate-aspartate shut-
tle to function. Which of the following is involved in this shuttle to
transfer electrons across the mitochondrial barrier?
A. Malate-aspartate antiporter
B. Malate-a-ketoglutarate antiporter
C. Glutamate-a-ketoglutarate antiporter
D. Aspartate-a-ketoglutarate symporter
E. Malate-glutamate symporter
A nsw ers
[27.1]
D. In this case the problem is insufficient oxygen reaches an area of
cardiac muscle. In the absence of sufficient oxygen, the use of the
electron transfer chain to generate ATP from ADP is severely com-
promised, and therefore all products feeding into that chain accumu-
late reducing the formation of tricarboxylic acid products. Fatty acid
oxidation, formation of acetyl-CoA from pyruvate oxidation of
ketone bodies, and oxidative phosphorylation are all decreased. In
glycolysis under reduced oxygen conditions, one pyruvate is con-
verted to lactate to reoxidize NADH to NAD+ to meet the requirement
for glycolysis to continue. Therefore, there is increased formation of
lactate.
[27.2]
C. The rates of both glucose utilization and ATP generation by gly-
colysis increase to compensate for the absence of sufficient ATP pro-
duction from oxidative phosphorylation as a result of oxygen
deprivation. Under these circumstances, ATP is used as rapidly as it
is made so it is not present in sufficient concentration to inhibit pyru-
vate kinase. Furthermore, fructose 1,6-bisphosphate tends to stimu-
late pyruvate kinase activity.
[27.3]
B. The malate-a-ketoglutarate antiporter carries malate from the
cytosol, where it is oxidized to oxaloacetate by mitochondrial malate
dehydrogenase forming NADH. In order for the malate-a-ketoglutarate
antiporter to function a molecule of a-ketoglutarate must be transported
from the mitochondrial matrix to the cytosol. The only other transporter
involved in this shuttle mechanism is the aspartate-glutamate antiporter.
None of the other suggested transporters is required in this shuttle
mechanism.
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