RuBisCO may exist in up to four different forms in nature. The most
abundant is form I found in all higher plants, red and brown algae, chemoautotrophic
bacteria, purple bacteria and cyanobacteria [12] and
[26]. The enzyme is composed of 8 large and 8 small subunits forming
a hexadecameric structure. Single large subunits (LSU, about 55 kDa)
form dimers and a tetramer of dimers. The small subunits (SSU, about
15 kDa) form tetramers which are placed on the top and the bottom
of the tetramer of the LSU. Each SSU makes contact with three LSU
and two SSU [26] and [27]. In the cyanobacterium Synechococcus
ACMM 323 it has been shown that the SSU is not essential for catalysis
but it stabilizes the complex structure of the enzyme, and contributes to
the maximal activity, efficiency and specificity [28]. Further subdivisions
of RuBisCO form I have been made based on amino acid sequences;
cyanobacteria possess forms IA and IB [23]. Form II of RuBisCO is present
in purple non-sulfur bacteria, several chemoautotrophic bacteria and
eukaryotic dinoflagellates. This form consists of only LSU forming dimers
[12]. Form III is found in archaea and it is relatively diverse, with
different structures such as LSU associated in dimers, octamers or
decamers. The final form IV is composed by enzymes that are similar
to RuBisCO sequences, but they neither use CO2 as substrate nor perform
the carboxylation reaction. Form IV is e.g. involved in sulfur metabolism
in the green sulfur bacterium Chlorobium tepidum [29], the
thermophilic bacterium Geobacillus kautophilus [30] as well as in other
bacteria.
RuBisCO may exist in up to four different forms in nature. The mostabundant is form I found in all higher plants, red and brown algae, chemoautotrophicbacteria, purple bacteria and cyanobacteria [12] and[26]. The enzyme is composed of 8 large and 8 small subunits forminga hexadecameric structure. Single large subunits (LSU, about 55 kDa)form dimers and a tetramer of dimers. The small subunits (SSU, about15 kDa) form tetramers which are placed on the top and the bottomof the tetramer of the LSU. Each SSU makes contact with three LSUand two SSU [26] and [27]. In the cyanobacterium SynechococcusACMM 323 it has been shown that the SSU is not essential for catalysisbut it stabilizes the complex structure of the enzyme, and contributes tothe maximal activity, efficiency and specificity [28]. Further subdivisionsof RuBisCO form I have been made based on amino acid sequences;cyanobacteria possess forms IA and IB [23]. Form II of RuBisCO is presentin purple non-sulfur bacteria, several chemoautotrophic bacteria andeukaryotic dinoflagellates. This form consists of only LSU forming dimers[12]. Form III is found in archaea and it is relatively diverse, withdifferent structures such as LSU associated in dimers, octamers ordecamers. The final form IV is composed by enzymes that are similarto RuBisCO sequences, but they neither use CO2 as substrate nor performthe carboxylation reaction. Form IV is e.g. involved in sulfur metabolismin the green sulfur bacterium Chlorobium tepidum [29], thethermophilic bacterium Geobacillus kautophilus [30] as well as in otherbacteria.
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