2. INTRODUCTION
• The Glyoxylate cycle is a sequence of anaplerotic
reactions (reactions that form metabolic
intermediates for biosynthesis) that enables an
organism to use substrates that enter central
carbon metabolism at the level of Acetyl Co-A as
the sole carbon source.
• Such substrates include fatty acids, alcohols, and
esters (often the products of fermentation), as
well as waxes, alkenes, and methylated
compounds.
• The pathway does not occur in vertebrates, but it
is found in plants and certain bacteria, fungi, and
invertebrates.
3. HISTORY
• The pathway was originally discovered in
bacteria [Kornberg,57], but later was found to
operate in some eukaryotic organisms as well.
• In plants, the cycle is involved in the
metabolism of storage oils during germination
of seeds [Brownleader,97].
• The cycle also operates in developing eggs of
nematodes, where it converts triacylglycerols
to carbohydrates [Patel,78].
4. What is GLYOXYLATE CYCLE?
• The plants and many microorganisms are
equipped with the metabolic machinery which
converts the fat into carbohydrates.
• It is a cyclic pathway in which 2 Acetyl Co-A
are converted into 1 molecule of Succinate.
• But not in animals, since they cannot carry out
the net synthesis of carbohydrates from fat.
5. • LOCATION :- It occurs in many bacterias,
plants, protists, and fungi.
• In plants, it occurs in the glyoxysomes, which
is a specialized peroxisome that carries out β-
oxidation of that Acetyl Co-A in the Glyoxylate
cycle.
• Human pathogen such as Mycobacterium
tuberculosis, uses Glyoxylate cycle to convert
lipids into carbohydrates.
6. REACTION
• The Glyoxylate cycle is an anabolic variant of
the Citric Acid cycle.
• Acetyl Co-A produced from fatty acid
oxidation condenses with Oxaloacetate to
give Citrate.
• Citrate is then converted to Isocitrate.
• Here, Isocitrate bypasses the TCA cycle and
cleave by Isocitratelyase to Succinate and
Glyoxylate.
7.
8. • Another molecule of Acetyl Co-A is now
utilized to combine with Glyoxylate to form
Malate. This reaction is catalysed by Malate
synthase.
• Finally, Malate dehydrogenase oxidises Malate
to Oxaloacetate and enters TCA cycle.
• It results in the conversion of two 2-C
fragments of Acetyl Co-A to 4-C compound,
Succinate.
9. • The Succinate produced within the
glyoxysome is transferred to the
mitochondria, where it enters TCA cycle and is
converted to Malate, which has 2 fates:-
i. It can be converted to Oxaloacetate in
mitochondria continuing TCA cycle.
ii. It can be transported to cytosol where it is
converted to Oxaloacetate for entry into
Gluconeogenesis.
• Bypass reaction= α- Ketoglutarate, Succinyl
Co-A.
