Elementary plant Biochemistry and Biotechnology (2+1)

The tricarboxylic acid cycle

• In 1937, Sir Hans Krebs, an English biochemist proposed a pathway consisting of a cycle of reactions through which acetyl
  
• CoA is converted to carbon dioxide and water and hence the cycle was named as Kreb's cycle.
• All the enzymes catalyzing the reactions of this cycle occur inside mitochondria (mitochondrial matrix) in contrast with those of glycolysis, which occur in the cytosol.
• Before pyruvate can enter the citric acid cycle, it must be oxidatively decarboxylated to acetyl CoA (active acetate).
• Three different enzymes working sequentially in a multienzyme complex catalyse this reaction .
• This formation of acetyl CoA from pyruvate by alpha-oxidative decarboxylation occurs in the mitochondrion following the formation of pyruvate in the cytosol during glycolysis.
• The reaction involves six cofactors: coenzyme A, NAD+, lipoic acid, FAD, thiamine pyrophosphate (TPP) and Mg2+.
TPP, FAD

CH3-CO-COOH+CoASH+NAD+ → CH3-CO-S-CoA+NADH+H++CO2 Lipoate, Mg2