RuBisCO, the carbon-fixing enzyme in the Calvin cycle, has the capacity
to catalyze two different reactions. In the carboxylation reaction,
it uses CO2 and ribulose-1,5-bisphosphate (RuBP) to produce two molecules
of 3-phosphoglycerate (3PGA). 3PGA is used in the regeneration
of RuBP in the Calvin cycle as the precursor for further cyanobacterial
carbon metabolism. In cyanobacteria, the regulation of 3PGA is performed
by sedoheptulose 1,7-bisphosphate proteins (SBPase proteins)
[25]. Besides the carboxylase activity, RuBisCO can also act as an oxygenase
resulting in photorespiration. In this case, RuBisCO uses O2 and
RuBP in order to form 3-phosphoglycerate and 2-phosphoglycolate.
The 2-phosphoglycolate is further converted to glycolate. The latter
can be metabolized by the C2 cycle, the glycerate pathway or through
decarboxylation.
RuBisCO, the carbon-fixing enzyme in the Calvin cycle, has the capacityto catalyze two different reactions. In the carboxylation reaction,it uses CO2 and ribulose-1,5-bisphosphate (RuBP) to produce two moleculesof 3-phosphoglycerate (3PGA). 3PGA is used in the regenerationof RuBP in the Calvin cycle as the precursor for further cyanobacterialcarbon metabolism. In cyanobacteria, the regulation of 3PGA is performedby sedoheptulose 1,7-bisphosphate proteins (SBPase proteins)[25]. Besides the carboxylase activity, RuBisCO can also act as an oxygenaseresulting in photorespiration. In this case, RuBisCO uses O2 andRuBP in order to form 3-phosphoglycerate and 2-phosphoglycolate.The 2-phosphoglycolate is further converted to glycolate. The lattercan be metabolized by the C2 cycle, the glycerate pathway or throughdecarboxylation.
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