Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

ADPglucose pyrophosphorylase (EC 2.7.7.27) from the cyanobacterium Synechocystis PCC 6803 was desensitized to the effects of allosteric ligands by treatment with the arginine reagent, phenylglyoxal. Enzyme modification by phenylglyoxal resulted in inactivation when the enzyme was assayed under 3P-glycerate-activated conditions. There was little loss of the catalytic activity assayed in the absence of activator. Pi, 3P-glycerate, and pyridoxal-P were able to protect the enzyme from inactivation, whereas substrates gave minimal protection. The protective effect exhibited by Pi and 3P-glycerate was dependent on effector concentration. MgCl2 enhanced the protection afforded by 3P-glycerate. The enzyme partially modified by phenylglyoxal was more resistant to 3P-glycerate activation and Pi inhibition than the unmodified form. Vmax at saturating 3P-glycerate concentrations and the apparent affinity of the enzyme toward Pi were decreased upon phenylglyoxal modification. Incorporation of labeled phenylglyoxal into the enzyme was proportional to the loss of activity. Pi and 3P-glycerate nearly completely prevented incorporation of the reagent to the protein. Results suggest that one arginine residue per mol of enzyme subunit is involved in the binding of allosteric effector in the cyanobacterial ADPglucose pyrophosphorylase.
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PMID:Involvement of arginine residues in the allosteric activation and inhibition of Synechocystis PCC 6803 ADPglucose pyrophosphorylase. 132 83

Electron transfer from P700 in photosystem I (PSI) particles from spinach to Anabaena sp. PCC 7119 flavodoxin has been studied using laser flash absorption spectroscopy. A non-linear protein concentration dependence of the rate constants was obtained, suggesting a two-step mechanism involving complex formation (k = 3.6 x 10(7) M-1.s-1) followed by intracomplex electron transfer (k = 270 s-1). The observed rate constants had a biphasic dependence on the concentrations of NaCl or MgCl2, with maximum values in the 40-80 mM range for NaCl and 4-12 mM for MgCl2. To our knowledge, this is the first time that the kinetics of PSI-dependent flavodoxin photoreduction have been determined.
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PMID:A laser flash absorption spectroscopy study of Anabaena sp. PCC 7119 flavodoxin photoreduction by photosystem I particles from spinach. 144 42

The large subunit (L) of ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) from Synechococcus PCC 6301 was expressed in Escherichia coli, purified as the octamer L8, and analyzed for its ability to tightly bind the transition state analog, 2-carboxyarabinitol 1,5-bisphosphate (CABP). [14C]CABP remained tightly bound to L8 after challenging with [12C]CABP and gel filtration, indicating that L8 alone without the small subunit (S) could tightly bind CABP. Binding of CABP to L8 induced a shift in the gel filtration profile due to apparent aggregation of L8. Aggregation did not occur with the L8S8-CABP complex nor with L8-CABP in the presence of 150 mM MgCl2. If ionic strength was increased with either KCl or MgCl2 during or after the binding of [14C]CABP to L8, [14C]CABP in the complex exchanged with [12C]CABP and was lost from the protein. Ionic strength strongly affected the rate constant (k4) for [14C]CABP dissociation from the L8-[14C]CABP complex, but had little effect on k4 for the L8S8-CABP complex. The differences in CABP binding characteristics between the L8-CABP and L8S8-CABP complexes demonstrate that S is intimately involved in maintaining the stability of the tight binding of CABP to the active site. These are the same interactions stabilizing the intermediate, 3-keto-2-carboxyarabinitol 1,5-bisphosphate, to native rubisco during CO2 fixation.
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PMID:Modulation of the tight binding of carboxyarabinitol 1,5-bisphosphate to the large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase. 191 Feb 81

Zymosan particles require opsonization for optimal interaction with granulocytes and activation of their respiratory burst. In the present study we evaluated the serum factors necessary for zymosan opsonization. First, zymosan was treated with either normal serum or hypogammaglobulinemic serum (HGS), which is deficient in immunoglobulins (Ig) but has a normal concentration of complement components. Using granulocyte chemiluminescence to assay opsonization, the activity of particles treated with HGS was 66 +/- 1.9% (mean +/- SEM) of that with normal serum (p less than 0.001), suggesting a role of Ig. HGS opsonic activity was restored to normal when the particles were also treated with IgG; however, neither heat-inactivated normal serum (56 degrees C, 30 min) nor pure human IgG alone had opsonic activity. The roles of the classical (CCP) and alternative (ACP) pathways of the complement system were also investigated. ACP activity seemed essential, since inactivation of the ACP (50 degrees C, 30 min) eliminated the activity of normal serum. However, when the ACP was intact, CCP action appeared to participate in opsonization, since selective CCP inactivation with EGTA and MgCl2 reduced the opsonic activity of normal serum by 26 +/- 3.3% (p less than 0.005). Thus, it is concluded that the ACP, CCP, and IgG all participate in zymosan opsonization.
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PMID:The role of complement and IgG on zymosan opsonization. 726 86

Laser-flash absorption spectroscopy has been used to investigate the kinetics of electron transfer from reduced cytochrome c6 and plastocyanin, isolated from Anabaena PCC 7119, to oxidized P700 in photosystem-I particles isolated from the same cyanobacterium and from spinach. For all metalloproteins and photosystems, the observed rate constant has a non-linear protein-concentration dependence, thus suggesting complex formation preceding electron transfer. Plastocyanin and cytochrome c6 have similar association constants for complex formation with spinach photosystem I, but the copper protein exhibits a higher intracomplex-electron-transfer rate constant (twofold). With Anabaena photosystem I, the two redox proteins are more effective with respect to both complex formation (5-10-fold) and electron transfer (1.5-4-fold) than with the spinach photosystem. In all cases, the observed rate constants for electron-transfer monotonically decrease with increasing NaCl or MgCl2 concentration. This is interpreted in terms of the involvement of attractive electrostatic interactions, which result in the initial collision complex having the most productive orientation for the electron transfer process, without a requirement for further reorientation. The magnitude of the response to MgCl2 suggests the occurrence of specific ion effects as well. In the absence of added salts, the reduction rate of oxidized P700 increases with pH from approximately 6 to 8, but decreases slightly at pH 8.5.
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PMID:A comparative laser-flash absorption spectroscopy study of Anabaena PCC 7119 plastocyanin and cytochrome c6 photooxidation by photosystem I particles. 850 8

The site-directed mutants of negative patches on silene plastocyanin (PC) were used to investigate the change of interactions between photosystem I (PSI) and PC during the course of evolution from cyanobacteria to plants. The net charges of two highly conserved negative patches (#42-45 and #59-61) on silene PC were systematically modified from -4 to +1. PSI complexes from cucumber and Chlamydomonas reinhardtii were efficient electron acceptors for silene PC. The increase of net charge on the negative patch (#42-45) of silene PC decreased the reduction rates of PSI from cucumber and Chlamydomonas, while the modification of the other negative patch (#59-61) had no effect. Though the addition of MgCl2 decreased the reduction rate of cucumber PSI, the decrease was severely diminished in the case of Chlamydomonas PSI, and the reduction rate increased with increasing concentration of MgCl2 when the net charge of the negative patch (#42-45) was modified to +1. The PSI complexes from Anabaena variabilis and Synechosystis sp. PCC 6803 were inefficient electron acceptors for silene PC and their rates were almost independent of the net charge of the negative patches, as well as the ionic strength of the reaction mixtures. Silene PC specifically cross-linked to the PsaF subunit of PSI complexes from cucumber, Chlamydomonas, Anabaena, and Synechosystis sp. PCC 6803. Modification of the negative patch (#42-45) inhibited the formation of cross-linked adducts in all the cases examined, whereas modification of the other negative patch (#59-61) had essentially no effect. Based on these results, the changes of electrostatic interactions between PC and PSI during the course of evolution from cyanobacteria to plants are discussed.
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PMID:Kinetic and cross-linking studies on the interactions of negative patch mutant plastocyanin from Silene pratensis with photosystem I complexes from cyanobacteria, green algae, and plants. 890 21

The response of cyanobacteria to a changing osmotic environment includes the accumulation of organic osmolytes such as glucosylglycerol. The activation of the enzymes involved in glucosylglycerol synthesis [glucosylglycerol-phosphate synthase (GGPS) and glucosylglycerol-phosphate phosphatase (GGPP)] in Synechocystis sp. strain PCC 6803 by various salts and salt concentrations was investigated in vitro. GGPS seemed to be the target for salt-mediated regulation of glucosylglycerol synthesis in vitro. GGPS activation was dependent on the concentration of NaCl, and a sigmoidal plot was obtained. Sensitivity to NaCl was markedly enhanced by low Mg+2 concentrations (optimal at 4 mM), but Mg2+ was not absolutely necessary for the Na+ stimulation. As in the case of NaCl, other salts (including MgCl2) stimulated GGPS. The relative order of GGPS activation in the presence of chloride by the cations at constant ionic strength was Li+ > Na+ > K+, Mg2+ Mn2+. No absolute dependence on ionic strength was observed in Mg2+/Na+-exchange experiments. The degree of activation by ions at various concentrations was positively related to the increasing destabilizing properties of the cations according to the Hofmeister rule, where chaotropic cations are most efficient. Cations were responsible for activation since chaotropic anions counteracted the activating effect of cations.
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PMID:Glucosylglycerol-phosphate synthase: target for ion-mediated regulation of osmolyte synthesis in the cyanobacterium synechocystis sp. strain PCC 6803 991 6

The effect of temperature on the activity and stability of ADPglucose pyrophosphorylase from Anabaena PCC 7120 was studied. Experimental optima temperatures were found around 37-40 degrees C or 42-45 degrees C, depending on the absence or the presence of allosteric effectors in the assay medium, respectively. In the range of temperature where the enzyme is stable, curved Arrhenius plots were obtained, indicating a transition temperature between 9 and 12 degrees C. Since these results were observed for both the forward and reverse reaction, with two different sets of substrates and two entirely different assay procedures, it seems unlikely that the effect can be on any component of the system other than the enzyme itself. Results suggest that cyanobacterial ADPglucose pyrophosphorylase undergoes conformational changes at different temperatures, rendering structures with different catalytic efficiencies. The different structures of the enzyme were visualized by emission fluorescence. ADPglucose pyrophosphorylase was irreversibly inactivated when exposed to temperatures above 40 degrees C. Inactivation was dependent on temperature and followed first order kinetics. The substrate, ATP, and the allosteric effectors, 3PGA and Pi, effectively protected the enzyme against thermal inactivation. Protection afforded by ATP was affected by MgCl2. These results suggest that the binding of the effectors to the enzyme resulted in conformational changes of the protein, rendering structures more stable to temperature treatments. Similar structures could be adopted by the enzyme in different environments, since the higher stability was observed in media containing either high ionic strength or high hydrophobicity.
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PMID:Studies on the effect of temperature on the activity and stability of cyanobacterial ADP-glucose pyrophosphorylase. 1136 19