Ribulose-1,5-bisphosphate carboxylase/oxygenase from thermophilic cyanobacterium Thermosynechococcus elongatus

Abstract

Ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) can be divided into two branches: the "red-like type" of marine algae and the "green-like type" of cyanobacteria, green algae, and higher plants. We found that the "green-like type" rubisco from the thermophilic cyanobacterium Thermosynechococcus elongatus has an almost 2-fold higher specificity factor compared with rubiscos of mesophilic cyanobacteria, reaching the values of higher plants, and simultaneously revealing an improvement in enzyme thermostability. The difference in the activation energies at the transition stages between the oxygenase and carboxylase reactions for Thermosynechococcus elongatus rubisco is very close to that of Galdieria partita and significantly higher than that of spinach. This is the first characterization of a "green-like type" rubisco from thermophilic organism.

Photorespiration and Rate Synchronization in a Phototroph-Heterotroph Microbial Consortium

“…for parameters used here (based on best approximations in comparison to known data) agrees well with measured values of inverse specificity [11,26,27].…”

“…Effectively, η is a branching function of O 2 and IC that determines how much photosynthetic product goes to synthesis of new biomaterial and how much to synthesis of soluble, excretable, organic carbon. Phototrophs may have a degree of control over the value of η either directly through the structure of RuBisCO itself [26,27] or through indirect machinery such as carbon capture mechanisms, so we treat γ 1 as a tunable parameter and study effects of its variation.…”

“…It is sometimes argued to be wasteful, e.g., [20], and possibly a relic of early earth history when levels of CO 2 were much higher than today, and levels of O 2 lower, so that the the ratio O 2 /CO 2 was presumably small. However, observations suggest it is not superfluous [28] and the orders of magnitude variability of γ across different species [11,26,27] suggests that there may be selective pressure at work. Photorespiration diverts carbon fixing power away from new biomass, but also note in fact the following: though glycolate has a lower degree of reduction (+3) than biomaterial (+4.7), its production requires 1/2 O 2 mole per Cmole of glycolate and hence, balancing electrons, also removes an additional two electrons per glycolate.…”

“…Proceeding as in the one species case, from (26) and (27) is damped (eventually) as e −Dt , that is, excess or deficience in the initial perturbation of total carbon and degree of reduction is removed from the system through outflow on the chemostat turnover time scale. Note again, thus, that we can therefore characterize the dynamics described by the five dimensional system (A15) if we can characterize the dynamics on a three dimensional subspace consisting of the null space of B, i.e., the subspace defined by ∼ C = 0, ∼ DoR = 0 (no net perturbation of total carbon or degree of reduction).…”

Mechanisms of carbon fixation and engineering for increased carbon fixation in cyanobacteria

“…Interestingly, RuBisCo purified from the cyanobacterium Phrochlorococcus marinus MIT9313 showed an activity of 0.41 μmol min −1 mg protein −1 [49] and RuBisCO from the cyanobacterium Thermosynechococcus elongatus expressed and purified in Escherichia coli a specific activity of 1.83 μmol min −1 mg protein −1 [50] compared to the PEPc activity of 8.84 μmol min −1 mg protein −1 observed in the cyanobacterium C. peniocystis [47]. PEPc is the primary CO 2 -fixing enzyme in C 4 and CAM plants [48] and [51].…”