Sedoheptulose-bisphosphatase

Some studies have suggested the SBPase may be part of a large (900 kDa) multi-enzyme complex along with a number of other photosynthetic enzymes.

In addition to being universally present in photosynthetic organism, SBPase is found in a number of evolutionarily-related, non-photosynthetic microorganisms.

[16] Moreso than other enzymes in the Calvin cycle, SBPase levels have a significant impact on plant growth, photosynthetic ability, and response to environmental stresses.

SBPase contains several catalytically relevant cysteine residues that are vulnerable to irreversible oxidative carbonylation by reactive oxygen species (ROS),[20] particularly from hydroxyl radicals created during the production of hydrogen peroxide.

[21] Carbonylation results in SBPase enzyme inactivation and subsequent growth retardation due to inhibition of carbon assimilation.

[18] Oxidative carbonylation of SBPase can be induced by environmental pressures such as chilling, which causes an imbalance in metabolic processes leading to increased production of reactive oxygen species, particularly hydrogen peroxide.

There are significant indications that transgenic plants which overexpress SBPase may be useful in improving food production efficiency by producing crops that are more resilient to environmental stresses, as well as have earlier maturation and higher yield.

[21] It is also likely that transgenic plants would be more resilient to osmotic stress caused by drought or salinity, as the activation of SBPase is shown to be inhibited in chloroplasts exposed to hypertonic conditions,[23] though this has not been directly tested.

Specifically, transgenic plants exhibited greater biomass and improved carbon dioxide fixation, as well as an increase in RuBisCO activity.

Reaction catalyzed by sedoheptulose-bisphosphatase
This is an illustration of the regulation of SBPase by ferredoxin and thioredoxin. [ 9 ]
Carbonylation of a cysteine residue via hydroxyl radical, analogous to how SBPase is inactivated by ROS.