RuBisCO

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RuBisCO
The Ubiquitous Enzyme
Created by Joe Harris June 22, 2005
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RuBisCO

• General Information
• RuBisCo stands for Ribulose 1,5-bisphosphate
  carboxylase/oxygenase.
• RuBisCO is a dual functional enzyme that is
  directly involved in photosynthesis as well as in
  photorespiration in plants.
• Its substrate is Ribulose 1,5-bisphosphate.

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RuBisCO

• General Information...
• In photosynthesis, it catalyzes the initial step
  in the fixation of carbon dioxide that produces
  2, 3-carbon molecules (PGA).
• During photorespiration it catalyzes O2 that
  produces 1 PGA molecule and a 2 carbon
  phosphoglycolate which is a competing oxygenation
  reaction.
• RuBisCO is found in higher plants,
  photosynthetic bacteria, algae and other bacteria.

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RuBisCO
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RuBisCO

• RuBisCOs Biochemistry
• RuBisCO is made up of 8 large subunits, and 8
  small subunits (hexadecamer), these are referred
  to as the barrels of the molecule.
• Large subunits usually weigh between 50 to 55
  kDa
• Small subunits usually weigh between 12 to 18
  kDa
• The large subunits associate as dimers. The
  N-terminus of one adjacent to the active site of
  the other.

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RuBisCO
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RuBisCO

• RuBisCOs Biochemistry
• The catalytic or active sites are present on the
  large subunits, but are unable to express
  catalytic activity unless the small subunits are
  also present.
• The large subunits are more than 80 homologous
  with each other.

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RuBisCO

• RuBisCOs Biochemistry
• The amino acids present in the active sites seem
  to be conserved and the catalytic properties of
  the enzyme seems to vary significantly between
  different organisms.
• In higher plants the enzyme is considerably
  specific, but highly inefficient. The turnover
  number for RuBisCO is only 3/sec. The opposite
  is observed for the Cyanobacteria enzyme.

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RuBisCO

• RuBisCos Biochemistry
• The genes for the large and small subunits occur
  consecutively on the chromosome and constitute a
  single operon.
• Large subunit - one gene in each circular DNA
  molecule of the chloroplasts.
• Small subunit - nuclear, small subunit genes are
  also multiple and comprise a multigene family of
  8 or more members.

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RuBisCO

• Gene Regulation
• Transcription of the genes for the small subunit
  is regulated by
• Environmental signals (light) and endogenous
  programs regulated by developmental and
  circadian aspects.
• External CO2 and O2 concentrations

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RuBisCO

• Regulation
• The activity of RuBisCO is regulated by another
  enzyme known as RuBisCO activase.
• There is a region in the amino acid sequence of
  RuBisCO activase that interacts with RuBisCO
  during the regulation process.

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RuBisCO

• Regulation...
• For RuBisCO to become catalytically active, it
  must be activated by carbamylation of the active
  site LYS residue which completes the binding for
  the fundamental Mg ion.
• The substrate and inhibitor levels are
  independent of RuBisCo because the enzyme exists
  in multiple forms.

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RuBisCO

• Regulation...
• Inhibitors
• Sugar phosphates
• Ribulose 1,5-bisphosphate (RuBP)
• 2-Carboxyarabinitol 1-Phosphate (CA1P)
• Xylulose 1,5-bisphosphate (XuBP, epimer of
  RuBP)
• PGA (phosphoglyceraldehyde)

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RuBisCO

• Regulation...
• Activator
• RuBisCO activase (inhibitor alleviator)
• Other factors (indirectly)
• ATP/ADP, Pi
• pH (transthylakoid)
• CO2, O2, temperature

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Any Questions?
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Thank You, The End
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Credits

• Kellogg, Elizabeth A., Nickolas D. Juliano 1997.
  The Structure and Function of RuBisCO and Their
  Implications for Systematic Studies. American
  Journal of Botany 84(3) 413-428.
• Jiang, Cai-Zhong, Steven R. Rodermel, and
  Richard M Snibles 1993. Photosynthesis, Rubisco
  Activity and Amount, and Their Regulation by
  Transcription in Senescing Soybean Leaves. Plant
  Physiology (1993) 101 105-112.
• Karp, Gerald 3rd ed. 2003. Cell and Molecular
  Biology John Wiley Sons, Inc. (text book).