[Serum, oral and gingival fluid levels of heat shock protein-70, cytokines and their autoantibodies by periodontal disease].

The study of 25 patients with periodontitis showed that the level of heat shock protein-70 (HSP70) and IL-1Β, IL-8 was increased in serum, buccal and gingival fluids as compared with healthy individuals, as well as the serum level of IgG autoantibodies both to HSP70 and to cytokines. In oral and gingival fluids sIgA autoantibodies to the same antigens were found. It was suggested that these autoantibodies can eliminate HSP-70 pro-inflammatory cytokines, thus regulating their levels in the inflammation area.

Bicarbonate is a native cofactor for assembly of the manganese cluster of the photosynthetic water oxidizing complex. Kinetics of reconstitution of O2 evolution by photoactivation.

Assembly of the inorganic core (Mn(4)O(x)Ca(1)Cl(y)) of the water oxidizing enzyme of oxygenic photosynthesis generates O(2) evolution capacity via the photodriven binding and photooxidation of the free inorganic cofactors within the cofactor-depleted enzyme (apo-WOC-PSII) by a process called photoactivation. Using in vitro photoactivation of spinach PSII membranes, we identify a new lower affinity site for bicarbonate interaction in the WOC. Bicarbonate addition causes a 300% stimulation of the rate and a 50% increase in yield of photoassembled PSII centers when using Mn(2+) and Ca(2+) concentrations that are 10-50-fold larger range than previously examined. Maintenance of a fixed Mn(2+)/Ca(2+) ratio (1:500) produces the fastest rates and highest yields of photoactivation, which has implications for intracellular cofactor homeostasis. A two-step (biexponential) model is shown to accurately fit the assembly kinetics over a 200-fold range of Mn(2+) concentrations. The first step, the binding and photooxidation of Mn(2+) to Mn(3+), is specifically stimulated via formation of a ternary complex between Mn(2+), bicarbonate, and apo-WOC-PSII, having a proposed stoichiometry of [Mn(2+)(HCO(3)(-))]. This low-affinity bicarbonate complex is thermodynamically easier to oxidize than the aqua precursor, [Mn(2+)(OH(2))]. The photooxidized intermediate, [Mn(3+)(HCO(3)(-))], is longer lived and increases the photoactivation yield by suppressing irreversible photodamage to the cofactor-free apo-WOC-PSII (photoinhibition). Bicarbonate does not affect the second (rate-limiting) dark step of photoactivation, attributed to a protein conformational change. Together with the previously characterized high-affinity site, these results reveal that bicarbonate is a multifunctional "native" cofactor important for photoactivation and photoprotection of the WOC-PSII complex.

The origin of atmospheric oxygen on Earth: the innovation of oxygenic photosynthesis.

The evolution of O(2)-producing cyanobacteria that use water as terminal reductant transformed Earth's atmosphere to one suitable for the evolution of aerobic metabolism and complex life. The innovation of water oxidation freed photosynthesis to invade new environments and visibly changed the face of the Earth. We offer a new hypothesis for how this process evolved, which identifies two critical roles for carbon dioxide in the Archean period. First, we present a thermodynamic analysis showing that bicarbonate (formed by dissolution of CO(2)) is a more efficient alternative substrate than water for O(2) production by oxygenic phototrophs. This analysis clarifies the origin of the long debated "bicarbonate effect" on photosynthetic O(2) production. We propose that bicarbonate was the thermodynamically preferred reductant before water in the evolution of oxygenic photosynthesis. Second, we have examined the speciation of manganese(II) and bicarbonate in water, and find that they form Mn-bicarbonate clusters as the major species under conditions that model the chemistry of the Archean sea. These clusters have been found to be highly efficient precursors for the assembly of the tetramanganese-oxide core of the water-oxidizing enzyme during biogenesis. We show that these clusters can be oxidized at electrochemical potentials that are accessible to anoxygenic phototrophs and thus the most likely building blocks for assembly of the first O(2) evolving photoreaction center, most likely originating from green nonsulfur bacteria before the evolution of cyanobacteria.

Bicarbonate requirement for the water-oxidizing complex of photosystem II.

It is well established that bicarbonate stimulates electron transfer between the primary and secondary electron acceptors, Q(A) and Q(B), in formate-inhibited photosystem II; the non-heme Fe between Q(A) and Q(B) plays an essential role in the bicarbonate binding. Strong evidence of a bicarbonate requirement for the water-oxidizing complex (WOC), both O2 evolving and assembling from apo-WOC and Mn2+, of photosystem II (PSII) preparations has been presented in a number of publications during the last 5 years. The following explanations for the involvement of bicarbonate in the events on the donor side of PSII are considered: (1) bicarbonate serves as an electron donor (alternative to water or as a way of involvement of water molecules in the oxidative reactions) to the Mn-containing O2 center; (2) bicarbonate facilitates reassembly of the WOC from apo-WOC and Mn2+ due to formation of the complexes MnHCO3+ and Mn(HCO3)2 leading to an easier oxidation of Mn2+ with PSII; (3) bicarbonate is an integral component of the WOC essential for its function and stability; it may be considered a direct ligand to the Mn cluster; (4) the WOC is stabilized by bicarbonate through its binding to other components of PSII.

Bicarbonate accelerates assembly of the inorganic core of the water-oxidizing complex in manganese-depleted photosystem II: a proposed biogeochemical role for atmospheric carbon dioxide in oxygenic photosynthesis.

The proposed role for bicarbonate (HCO(3)(-)) as an intrinsic cofactor within the water-oxidizing complex (WOC) of photosystem II (PSII) [Klimov et al. (1997) Biochemistry 36, 16277-16281] was tested by investigation of its influence on the kinetics and yield of photoactivation, the light-induced assembly of the functional inorganic core (Mn(4)O(y)Ca(1)Cl(x)) starting from the cofactor-depleted apo-WOC-PSII center and free Mn(2+), Ca(2+), and Cl(-). Two binding sites for bicarbonate were found that stimulate photoactivation by accelerating the formation and suppressing the decay, respectively, of the first light-induced assembly intermediate, IM(1) [apo-WOC-Mn(OH)(2)(+)]. A high-affinity bicarbonate site (K(D)

Bicarbonate protects the donor side of photosystem II against photoinhibition and thermoinactivation.

The rate of photoinhibition of photosystem II (PSII) activities (photoinduced change of chlorophyll fluorescence yield, deltaF, and photoreduction of 2,6-dichlorophenol-indophenol) in O2-evolving pea subchloroplast membrane fragments in medium depleted of CO2 was considerably decreased upon addition of 5 mM NaHCO3 before the light treatment. A similar effect was observed when 100 microM MnCl2 was added before the photoinhibition. In PSII membrane fragments depleted of Mn, the preillumination led to irreversible loss of the capability of PSII to be reactivated by Mn2+, and the rate of the photoinhibition was decreased by a factor of 2 or 5 if the pre-illumination was done in the presence of 0.2 microM MnCl2 (approximately 4 Mn per PSII reaction center) added alone or in combination with 5 mM NaHCO3, respectively. A similar protective effect of bicarbonate was also revealed in the dark, during thermoinactivation of O2-evolving PSII at 40 degrees C: the rate of thermoinactivation of deltaF was decreased by a factor of 3 if 5 mM NaHCO3 was added to the medium. The results are consistent with the idea that bicarbonate is an essential component of the Mn-containing water-oxidizing complex of PSII, which decreases its susceptibility to photoinhibition and thermoinactivation.

Bicarbonate requirement for the donor side of photosystem II.

Suppression of electron flow (and its subsequent restoration with 3-10 mM NaHCO3) on the donor side of photosystem II is shown upon either a partial depletion of pea subchloroplast membranes in bicarbonate or the addition of 5-20 microM formate. At higher concentrations (5 mM) formate induces the known 'bicarbonate effect' on the acceptor side of photosystem II. In preparations depleted of manganese the restoration of electron flow with 0.1-0.2 microM MnCl2 (2-4 Mn per photosystem II reaction center) occurs only in the presence of bicarbonate and it is accompanied by an increased functional binding of manganese. Restoration of electron flow with diphenylcarbazide or NH2OH does not require the addition of NaHCO3. It is suggested that bicarbonate participates in the formation of the Mn-cluster capable of water oxidation or serves as a substrate for the water-oxidizing center.

Effects of bicarbonate and formate on the donor side of Photosystem 2.

Sodium formate at concentration of 5-20 µM suppresses electron flow on the donor side of Photosystem 2 (PS 2) in pea subchloroplast membranes (DT-20) which is revealed by inhibition of photoinduced changes of chlorophyll fluorescence yield related to photoreduction of QA and pheophytin (the primary and intermediary electron acceptors) and oxygen evolution and the increase of absorbance changes related to photooxidation of P680, the primary electron donor, under continuous illumination. These activities are also inhibited upon partial depletion of bicarbonate in the medium and restored by the addition of 0.1-10 mM NaHCO3. At concentrations higher than 20 µM formate induces the known bicarbonate effect on the acceptor side of PS 2 which dominates at millimolar concentrations of the agent. In Tris-treated (Mn-depleted) DT-20 the restoration of electron flow with 0.2 µM MnCl2 (4 Mn atoms per one PS 2 reaction center) in the medium depleted of bicarbonate is efficient only after the addition of 5 mM NaHCO3. The restoration in the presence of NaHCO3 is accompanied by an increased functional binding of Mn(2+) to PS 2 membranes which is confirmed by experiments on removal of added Mn(2+) by either sedimentation or the addition of EDTA. Pre-illumination increases the Mn binding in the presence of bicarbonate. The data show that the bicarbonate effect on the donor side of PS 2 is related to a relatively low-affinity bound pool of bicarbonate. It is suggested that bicarbonate takes part in the formation of the Mn-cluster capable of water oxidation as an obligatory ligand or through modification of the binding site(s) of Mn.