decomposition and carbon dissolution in marine resources, namely the oceans,
although others, such as permafrost, have been progressively recognized as
important in the future regulation of atmospheric CO 2 levels [9]. Biological processes are vital in the carbon cycle. There are multiple biological processes related
with CO 2 release and uptake and within these, enzymes that carry these reactions.
Brief descriptions of some of the most interesting enzymes that may be used in
technological systems using CO 2 are given below.
Probably the most renowned biological process is photosynthesis, a process
common to plants, algae and cyanobacteria. In the carbon cycle, one of the
first enzymes whose importance was recognized is RuBisCO (ribulose
1,5-bisphosphatecarboxylase/oxygenase). This ancient enzyme allows carbon
fixation and biomass accumulation through the catalysis of its initial step which is
the CO 2 conversion into hydrocarbons, namely through the carboxylation of
ribulose 1,5-bisphosphate (RuBP) and further cleavage, forming two molecules of
3-phospho-glycerate (3PG) [10, 11]. Although being an essential enzyme to Earth
as we know it, and apparently appealing to incorporate in biotechnological systems,
this enzyme presents some limitations, namely the reaction has low rate, it depends
on an activation step by another enzyme, the reaction has multiple steps and it is
easily inhibited [10, 12]. Also, oxygen competes with CO 2 and the specificity
depends on several factors, including the ratio of CO 2 to O 2 in the vicinity of the
enzyme [13]. The activation of the enzyme requires a complex mechanism
depending on the presence of Mg
2+ ion and a suitable charge distribution around
this [14]. The enzyme is active when a conserved Lys201 of the large subunit binds
CO 2 together with the Mg
2+ ion-producing a carbamate [14]. RuBisCO is not easy
to handle, not only due to its mechanism but also its structure, since it is a multimeric structure, presenting large (L, approx. 50 to 55 kDa) and small (S, approx.
12 to 18 kDa) subunits. The enzyme presents three forms, characteristic of
organisms from, respectively, proteobacteria, cyanobacteria, algae and vascular
plants (Form I, the most abundant), chemoautotrophs, proteobacteria and
dinoflagellated algae (Form II) and archaea (Form III) where the main catalytic
dimeric subunit, L, may present structures with L 2 to (L 2 ) 5 , [12].
Another well-known enzyme class is carbonic anhydrase (CA) making a
bridge between the geological and biological parts of the carbon cycle. CAs
catalyse the reversible conversion of CO 2 into hydrogen carbonate ion which is
very appealing to pursue its incorporation in atmospheric CO 2 mitigation systems
[15]. CAs participate in several functions besides CO 2 transport and conversion to
bicarbonate, namely, in respiration, pH regulation, biosynthesis, among others, and
are found in all known living organisms. These are metalloenzymes, usually
bearing Zn
2+ in their active site (Fe and Cd were also found) and are observed in
different families with different structures that evolved towards a common activity
[16, 17]. Among those, the a-CA which are found in animals, plants, vertebrates,
bacteria and algae, present high activities, and good stability, being soluble and
easily expressed, making these promising to be incorporated in CO 2 mitigation
systems using diverse strategies [15, 18–20].
86
C. M. Cordas et al.
although others, such as permafrost, have been progressively recognized as
important in the future regulation of atmospheric CO 2 levels [9]. Biological processes are vital in the carbon cycle. There are multiple biological processes related
with CO 2 release and uptake and within these, enzymes that carry these reactions.
Brief descriptions of some of the most interesting enzymes that may be used in
technological systems using CO 2 are given below.
Probably the most renowned biological process is photosynthesis, a process
common to plants, algae and cyanobacteria. In the carbon cycle, one of the
first enzymes whose importance was recognized is RuBisCO (ribulose
1,5-bisphosphatecarboxylase/oxygenase). This ancient enzyme allows carbon
fixation and biomass accumulation through the catalysis of its initial step which is
the CO 2 conversion into hydrocarbons, namely through the carboxylation of
ribulose 1,5-bisphosphate (RuBP) and further cleavage, forming two molecules of
3-phospho-glycerate (3PG) [10, 11]. Although being an essential enzyme to Earth
as we know it, and apparently appealing to incorporate in biotechnological systems,
this enzyme presents some limitations, namely the reaction has low rate, it depends
on an activation step by another enzyme, the reaction has multiple steps and it is
easily inhibited [10, 12]. Also, oxygen competes with CO 2 and the specificity
depends on several factors, including the ratio of CO 2 to O 2 in the vicinity of the
enzyme [13]. The activation of the enzyme requires a complex mechanism
depending on the presence of Mg
2+ ion and a suitable charge distribution around
this [14]. The enzyme is active when a conserved Lys201 of the large subunit binds
CO 2 together with the Mg
2+ ion-producing a carbamate [14]. RuBisCO is not easy
to handle, not only due to its mechanism but also its structure, since it is a multimeric structure, presenting large (L, approx. 50 to 55 kDa) and small (S, approx.
12 to 18 kDa) subunits. The enzyme presents three forms, characteristic of
organisms from, respectively, proteobacteria, cyanobacteria, algae and vascular
plants (Form I, the most abundant), chemoautotrophs, proteobacteria and
dinoflagellated algae (Form II) and archaea (Form III) where the main catalytic
dimeric subunit, L, may present structures with L 2 to (L 2 ) 5 , [12].
Another well-known enzyme class is carbonic anhydrase (CA) making a
bridge between the geological and biological parts of the carbon cycle. CAs
catalyse the reversible conversion of CO 2 into hydrogen carbonate ion which is
very appealing to pursue its incorporation in atmospheric CO 2 mitigation systems
[15]. CAs participate in several functions besides CO 2 transport and conversion to
bicarbonate, namely, in respiration, pH regulation, biosynthesis, among others, and
are found in all known living organisms. These are metalloenzymes, usually
bearing Zn
2+ in their active site (Fe and Cd were also found) and are observed in
different families with different structures that evolved towards a common activity
[16, 17]. Among those, the a-CA which are found in animals, plants, vertebrates,
bacteria and algae, present high activities, and good stability, being soluble and
easily expressed, making these promising to be incorporated in CO 2 mitigation
systems using diverse strategies [15, 18–20].
86
C. M. Cordas et al.