PYRUVATE METABOLISM
Introduction. In glycolysis, NADH is produced in the cytosol, but in order to accumulate it in the form of ATP, we need it to enter the mitochondria. The problem is that the inner membrane of the mitochondria is very permeable, which means that NADH cannot be used directly in the respiratory chain.
To enter the mitochondria, NADH requires a series of indirect mechanisms called shuttles, notably the glyceron 3-phosphthane shuttle and the malate / aspartate shuttle.
Glycerol 3-phosphate shuttle. In glycolysis, NADH is produced in the cytosol, which is oxidized to NAD +, which will reduce phosphohydroxybenote, which will form glycerol 3- phosphate through the enzyme glycerol 3-phosphate dehydrogenase.
This occurs in the cytosol, but glycerol 3-phosphthane has to enter the inner membrane of the mitochondria, where it is re-oxidized, thanks to a mitochondrial isoenzyme.
Therefore, there are two glycerol 3-phosphate dehydrogenase enzymes: one in the cytosol and another inside the mitochondrial, that is, they are isoenzymes.
Glycerol 3-phosphate dehydrogenase in the mitochondria is dependent on FAD, which is transformed to FADH2 by losing two electrons.
Therefore, the NADH that we have in the cytosol is the one that is going to be in charge of forming the FADH2. This makes the 2.5 ATP that we had become 1.5 ATP, that is, the performance is lower.
Intermembrane space(P side)
Glycolysis
NAD+ NADH+H+ cytosolic glycerol3-phosphate dehydrogenase
CHOH c=o Dihydroxyacetone phosphate @-O-2H
Glycerol'3- phosphate CH2OH CHOH CH-O- FAD FADH
mitochondrial glycerol3-phospl dehydrogenase
QH2
11
Matrix(N side)
Malate-aspartate shuttle.The NADH produced in glycolysis is found in the cytosol. This NADH is oxidized to NAD + in exchange for oxaloacetate being reduced to malate by an enzyme, called malate dehydrogenase.
1
NADH cannot penetrate the interior of the mitochondrion, unlike malate, which penetrates the mitochondria thanks to a facilitated diffusion transport. Once the malate is inside, it is oxidized to oxaloacetate with the malate dehydrogenase enzyme from the matrix.
Oxaloacetate gives rise to aspartate at the cost of glutamic acid to a-acetoglutarate. This transmission reaction is catalyzed by glutamic-oxaloacetate-transaminase (GOT).
The aspartate, which is found inside the mitochondria, goes out into the cytosol through a process of facilitated diffusion, through a transporter that removes aspartic while it enters glutamic.
Once in the cytosol, aspartate is transformed into oxaloacetate. In the same way that a-
ketoglutarate leaves the cytosol to close the cycle through a cotransport with malate, which enters the mitochondria. Thus, it is possible to close the cycle.
ASPARTATO
ASPARTATO
GLU GOT -Cotogwt
GLU
107 a-cetogwt
HAUR
CYALACETATO
OXALACETATO NADH+H+
Hatato DH
Nalato dH
NALATO
MALATO
NAD
M ATRiZ MiTOCOUORiAL
CiTOSOL
Entry of other sugars in the glycolytic pathway. Glucose can come from glycogen or it can be ingested through diet (essential contribution) Glucose 1 This glucose will give rise to glucose 6- Galactose phosphate which, later, will be transformed into fructose 6-phosphate. The latter passes to fructose 1,6-bisphosphate and, finally, to 3- 1 phosphoglyceraldehyde. F-1,6-BP
Galactose is considered a source of glucose for Fructose DHAP GAP Fructose glycolysis. liver li