What are the Fate of Pyruvate Molecules after Glycolysis?

Glycolysis is taking place in Cytoplasm. So Pyruvate is generated in Cytoplasm. This is to be transported into mitochondria by a Pyruvate transporter. It is a simport, where the hydrogen ion is a transporter. Here two different enzymes are involved based on the condition. They are Pyruvate dehydrogenase and Lactate dehydrogenase enzymes. There are 2 different conditions are monitored by the Pyruvate fate.

fate of pyruvate

  • Anaerobic Condition (Absence of Oxygen) → It converts Glucose into Lactate
  • Aerobic Condition (Presence of Oxygen) → It converts Glucose into Acetyl~CoA

Anaerobic Condition

In Myocytes in muscles, the Pyruvate is converted into Lactate. In the presence of the enzyme “Lactate dehydrogenase (LDH)”. In the reaction, NADH+H+ is consumed. Lactate Dehydrogenase (LDH) is a classical example for Isoenzyme (or) Isozyme. The molecular weight is 1, 40,000.

Pyruvate → Lactate + NAD+

Aerobic Condition

In the presence of oxygen the Pyruvate is converted into Acetyl~coA molecule. This reaction is catalyzed by “Pyruvate dehydrogenase” complex (PDH complex).

Pyruvate + CoenzymeA  → Acetyl~coA + NADH + H+ + CO2

pdh complex structure

About Pyruvate Dehydrogenase Enzyme

  • PDH is a multienzyme complex
  • The molecular weight of the PDH complex in Escherichia coli is 48,00,000.
  • PDH complex is located in the Matrix Space of Mitochondria of the erythrocytes in the cytoplasm of the prokaryotes.
  • The Enzyme contains 3 enzymatic sub-units and 5 co-enzymes.

Enzymatic subunits of PDH Complex:

  • Pyruvate dehydrogenase (or) Pyruvate decarboxylase [E1]
  • Dihydrolipoyl transacetylase [E2]
  • Dihydrolipoyl dehydrogenase [E3]

CoEnzymes of PDH complex:

  • Thiamine pyrophosphate (TPP)
  • Lipoic acid
  • Flavin Adenine Dinucleotide (FAD)
  • CoEnzyme~A
  • Nicotinamide Adenine Dinucleotide (NAD+)

Mechanism of Pyruvate Dehydrogenase Complex

There is 5 successive stages in the conversion of Pyruvate into Acetyl~coA. These are as follows.

Fate of Pyruvate Molecule after Glycolysis: Pyruvate Dehydrogenase complex

Step 1:

Pyruvate loses its carboxyl group as it reacts with the bound TPP of Pyruvate of E1 subunit to form the hydroxyl Methyl derivative of Thiazole ring of TPP.

Step 2:

The hydrogen atom and acetyl group are transferred to the oxidized form of lipoyl group of Coenzyme E2 to form 6-acetyl thioester of the reduced lipoyl groups.

Step 3:

A molecular CoEnzymeA reacts with the acetyl derivative of E2 to produce acetyl~coA and the fully reduces form of lipoyl group. the Acetyl~coA is involved in the TCA cycle.

Step 4:

The fully reduced form of E2 is acted upon by E3 which promotes the transfer of hydrogen atom from reduced lipoyl groups to the FAD prosthetic group of E3.

Step 5:

In this last stage the reduced group of E3 transfer hydrogen to NAD+ forming NADH.

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