Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Gatekeeping”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 847 records · Page 47Linked to original sources
PubMed1989

Genetic diagnosis. Implications for medical practice.

Genetic diagnostic techniques increasingly permit the detection of predisposition to illness long before the onset of the disease process itself. Medicine is on the verge of becoming a predictive science as well as a diagnostic and therapeutic one. Genetic diagnosis could have profound effects on many aspects of our health care system, including the prestige and effectiveness of preventive medicine, the competitive behavior of health care organizations and insurance companies, access to private health insurance, the ability of primary care physicians to serve as gatekeepers, and other matters. This article examines the range of potential effects of the new genetic diagnostics on the organization and financing of health care. For purposes of illustration the authors examine in detail the possible consequences of genetic tests for predisposition to two diseases: Reye's Syndrome and lung cancer in smokers.

Cost-Benefit Analysis↗
PubMed2000

Health technology assessment in Denmark.

The Danish healthcare services are mainly provided by public sector institutions. The system is highly decentralized. The state has little direct influence on the provision of healthcare services. State influence is exercised through legislation and budget allocations. The main task of the state is to initiate, coordinate, and advise. Counties, which run the hospitals, also decide on the placement of services. The hospital sector is controlled within the framework of legislation and global budgets. General practitioners occupy a central position in the Danish healthcare sector, acting as gatekeepers to the rest of the system. The system works well, and its structure has resulted in steady costs of health care for a long period. There is no regulatory mechanism in the Danish health services requiring use of health technology assessment (HTA) as a basis for policy decisions, planning, or administrative procedures. However, since the late 1970s a number of comprehensive assessments of health technology have formed the basis for national health policy decisions. In 1997, after years of public criticism of the quality of hospital care and health technologies, and on the basis of a previously developed national HTA strategy, a national institute for HTA (DIHTA) was established. There seems to be a growing awareness of evidence-based healthcare among health professionals and a general acceptance of health economic analyses as a basis for health policy decision making. This progress is coupled with growing regional HTA activity in the health services. HTA seems to have a bright future in Denmark.

Adolescent↗
PubMed2000

Health technology assessment in The Netherlands.

The Dutch healthcare system is not a single overall plan, but has evolved from a constantly changing mix of institutions, regulations, and responsibilities. The resulting system provides high-quality care with reasonable efficiency and equal distribution over the population. Every Dutch citizen is entitled to health care. Health insurance is provided by a mix of compulsory national insurance and public and private insurance schemes. Hospitals generally have a private legal basis but are heavily regulated. Supraregional planning of high-tech medical services is also regulated. Hospitals function under fixed, prospective budgets with regulation of capital investments. Independent general practitioners serve a gatekeeper role for specialist and hospital services and are paid by capitation or fee for service. Specialists are paid by fee for service. All physicians' fees are controlled by the Ministry of Economic Affairs. Coverage of benefits is an important method of controlling the cost of services. There is increasing concern about health care quality. Health technology assessment (HTA) has become increasingly visible during the last 15 years. A special national fund for HTA, set up in 1988, has led to many formal and informal changes. HTA has evolved from a research activity into policy research for improving health care on the national level. In 1993 the government stated formally that enhancing effectiveness in health care was one of its prime targets and that HTA would be a prime tool for this purpose. The most important current issue is coordination of HTA activities, which is now undertaken by a new platform representing the important actors in health care and HTA.

Community Health Planning↗
PubMed2000

Health technology assessment in the United Kingdom.

The National Health Service (NHS) provides universal health coverage for all British citizens. Most services are free of charge, although modest copayments are sometimes applied. About 11% of the population also has private insurance. General practitioners, generally the first point of contact for accessing the system, are independent contractors who serve as gatekeepers for specialist and hospital services and enjoy substantial clinical autonomy. Hospitals are public and are regionalized, but the 1990 reforms made them self-governing trusts that contract with local purchasers (health authorities and general practitioner fundholders). Reforms beginning in 1990 moved the NHS away from a centralized administrative structure to more pluralistic arrangements in which competition, as well as management, influences how services develop. Health technology and health technology assessment (HTA) have gained increasing attention in the NHS during this period, as part of a wider NHS Research and Development (R&D) Strategy. The strategy promotes a knowledge-based health service with a strong research infrastructure and the capacity to critically review its own needs. HTA is the largest and most developed of the programs within the strategy. It has a formal system for setting assessment priorities involving widespread consultation within the NHS, and a National Co-ordinating Centre for Health Technology Assessment. The strategy supports related centers such as the U.K. Cochrane Centre and the NHS Centre for Reviews and Dissemination. A hallmark of the HTA program is strong public participation. The United Kingdom has made a major commitment to HTA and to seeking effective means of reviewing and disseminating evidence.

Delivery of Health Care↗
PubMed2000

Health technology diffusion rates. Statins, coronary stents, and MRI in England.

OBJECTIVE: To analyze the rates and influences on the adoption of three selected health technologies: statins, coronary stents, and magnetic resonance imaging (MRI). METHODS: A retrospective diffusion study using primary care prescribing data and questionnaire responses from acute hospital trusts in the West Midlands region (population 5.3 million or 10% of England). RESULTS: The selected technologies had markedly different diffusion curves. Statins diffused rapidly soon after launch. Coronary stents were initially used 6 years after first availability, but within 2 years all responding hospitals reported using them. MRI scanners were initially purchased 6 years after first availability with a subsequently slow rate of diffusion, and are still absent from some hospitals. Influences on the adoption of each technology were different. Commercial marketing was reported as a major influence on the diffusion of statins but not at all on MRIs. Cost impact was a major negative influence on the diffusion of MRI scanners and statins, whereas enthusiastic individuals were key to the diffusion of stents. CONCLUSIONS: Influences on adoption and consequent diffusion rates are very different for different health technologies. It is not at all clear that such diffusion patterns relate well to an optimum timing rate. This has important implications for technology gatekeepers in health care.

Anticholesteremic Agents↗
PubMed2006

Inoculating against barbarism? State medicine and immigrant policy in turn-of-the-century Argentina.

The border in turn-of-the-century Argentina was a place of heightened anxiety. State officials ignored the nation's vast land borders and focused on the port, located in the capital city of Buenos Aires, which attracted nearly six million European immigrants in the decades after 1870. Federal authorities were seeking to attract new immigrants and yet they were terrified that opening their gates would allow entry among the potential citizenry a new category of "toxins" dangerous to the national body. The authorities hired physicians as gatekeepers to identify desirable and undesirable traits that went beyond the definition of communicable disease. Science and medicine appeared to provide a means of legitimating a variety of attempts by the state to control the makeup of the population; in reality, the state's power to inspect immigrants for disease, racial toxins, social upheaval, and political instability was minimized by realistic decisions to open borders and by a weak and limited ability to control the influx of people. Alongside calls for immigrant selection there coexisted a strong trend in political discourse that sought to build a unified, homogenous national culture by accepting and assimilating the foreign masses. Both approaches, however, had similar goals--the material progress of the nation, the advancement of Argentina's "civilization," and the erasure of traces of "foreignness" among the new population.

Argentina↗
PubMedDate not supplied

Use of on-line medical command to randomize patients in a prehospital research study.

OBJECTIVE: To describe the efficiency of using on-line medical command (OLMC) to conduct a prospective, randomized clinical trial addressing safety and patient enrollment. DESIGN, SETTING, AND PARTICIPANTS: Prospective design using OLMC to randomize adult asthmatics into one of three treatment groups. After verifying inclusion and exclusion criteria, OLMC physicians removed a covering label on study sheets and ordered the treatment specified underneath the label that had been assigned in a random sequence. RESULTS: A total of 204 patients were seen with dyspnea and wheezing during the three-month study. Of these, 68 (33%) were excluded from the study. Of the 136 (67%) patients who were eligible for study, 87 were enrolled (enrollment efficiency 64%), with 79 fully evaluable (evaluable efficiency 91%). The study safety was 100% because no enrolled patients met any exclusion criteria. CONCLUSIONS: The design was random and prospective, with patient entry blinded, using paramedics to enroll patients and OLMC physicians as gatekeepers, thus ensuring appropriate patient eligibility and study-arm assignment. Use of OLMC physicians to perform prospective randomized studies is safe and efficient, and results in a high yield of evaluable patients.

Adolescent↗
PubMed2000

Directed molecular evolution of cytochrome c peroxidase.

Cytochrome c peroxidase (CCP) from Saccharomyces cerevisiae was subjected to directed molecular evolution to generate mutants with increased activity against the classical peroxidase substrate guaiacol, thus changing the substrate specificity of CCP from the protein cytochrome c to a small organic molecule. After three rounds of DNA shuffling and screening, mutants were isolated which possessed a 300-fold increased activity against guaiacol and an up to 1000-fold increased specificity for this substrate relative to that for the natural substrate. In all of the selected mutants, the distal arginine (Arg48), which is fully conserved in the superfamily of peroxidases, was mutated to histidine, showing that this mutation plays a key role in the significant increase in activity against phenolic substrates. The results suggest that, in addition to stabilizing the reactive intermediate compound I, the distal arginine plays an important role as a gatekeeper in the active site of CCP, controlling the access to the ferryl oxygen and the distal histidine. Other isolated mutations increase the general reactivity of the peroxidase or increase the intracellular concentration of the active holo form, allowing their selection under the employed screening conditions. The results illustrate the ability of directed molecular evolution technologies to deliver solutions to biochemical problems that would not be readily predicted by rational design.

Alanine↗
PubMed1991

Calcium limits substrate accessibility or reactivity at the manganese cluster in photosynthetic water oxidation.

The structural changes which the tetramanganese cluster responsible for catalyzing photosynthetic water oxidation undergoes upon calcium depletion of photosystem II membranes via the citrate extraction method has been further characterized. The modified multiline EPR signal which forms has been further identified with an S2' oxidation state. The increased number of hyperfine lines (at least 26) and 25% narrower hyperfine splittings from 55Mn versus the normal S2-state signal indicate a redistribution of spin density, most likely within a spin-coupled tetranuclear Mn cluster. A simpler binuclear Mn description for this signal can be eliminated. Slow conformational changes occur over 30 min which cause subtle changes in the hyperfine structure. Comparison to the modified multiline signals produced by Sr2+ replacement of Ca2+ and NH3-treated PSII reveal similarities suggestive of formation of the same spin S = 1/2 state. Substrate accessibility in the dark S1' state, measured as Mn2+ release upon incubation with NH2OH, is increased by 10-fold over calcium-containing PSII centers. Diphenylcarbazide, an efficient electron donor to Tyr-Z+ only in PSII membranes in which Mn is removed or dislocated, was found to donate electrons in Ca(2+)-depleted PSII, indicating altered accessibility or reactivity. These results suggest a possible "gatekeeper" role for Ca2+ in limiting access of substrate water to the Mn cluster. These changes are not due to release of the three extrinsic polypeptides of PSII which remain bound. Citrate treatment also causes partial air oxidation of the reaction-center Fe2+ ion, associated with the quinone electron acceptors. The resulting Fe3+ possesses an EPR signal at g = 4.37 arising from conversion to a rhombic symmetry ligand field.

Calcium↗
PubMed2001

Interaction of acetylene and cyanide with the resting state of nitrogenase alpha-96-substituted MoFe proteins.

The nitrogenase MoFe protein contains the active site metallocluster called FeMo-cofactor [7Fe-9S-Mo-homocitrate] that exhibits an S = 3/2 EPR signal in the resting state. No interaction with FeMo-cofactor is detected when either substrates or inhibitors are incubated with MoFe protein in the resting state. Rather, the detection of such interactions requires the incubation of the MoFe protein together with its obligate electron donor, called the Fe protein, and MgATP under turnover conditions. This indicates that a more reduced state of the MoFe protein is required to accommodate substrate or inhibitor interaction. In the present work, substitution of an arginine residue (alpha-96(Arg)) located next to the active site FeMo-cofactor in the MoFe protein by leucine, glutamine, alanine, or histidine is found to result in MoFe proteins that can interact with acetylene or cyanide in the as-isolated, resting state without the need for the Fe protein, or MgATP. The dithionite-reduced, resting states of the alpha-96(Leu)-, alpha-96(Gln)-, alpha-96(Ala)-, or alpha-96(His)-substituted MoFe proteins show an S = 3/2 EPR signal (g = 4.26, 3.67, 2.00) similar to that assigned to FeMo-cofactor in the wild-type MoFe protein. However, in contrast to the wild-type MoFe protein, the alpha-96-substituted MoFe proteins all exhibit changes in their EPR spectra upon incubation with acetylene or cyanide. The alpha-96(Leu)-substituted MoFe protein was representative of the other alpha-96-substituted MoFe proteins examined. The incubation of acetylene with the alpha-96(Leu) MoFe protein decreased the intensity of the normal FeMo-cofactor signal with the appearance of a new EPR signal having inflections at g = 4.50 and 3.50. Incubation of cyanide with the alpha-96(Leu) MoFe protein also decreased the FeMo-cofactor EPR signal with concomitant appearance of a new EPR signal having an inflection at g = 4.06. The acetylene- and cyanide-dependent EPR signals observed for the alpha-96(Leu)-substituted MoFe protein were found to follow Curie law 1/T dependence, consistent with a ground-state transition as observed for FeMo-cofactor. The microwave power dependence of the EPR signal intensity is shifted to higher power for the acetylene- and cyanide-dependent signals, consistent with a change in the relaxation properties of the spin system of FeMo-cofactor. Finally, the alpha-96(Leu)-substituted MoFe protein incubated with (13)C-labeled cyanide displays a (13)C ENDOR signal with an isotropic hyperfine coupling of 0.42 MHz in Q-band Mims pulsed ENDOR spectra. This indicates the existence of some spin density on the cyanide, and thus suggests that the new component of the cyanide-dependent EPR signals arise from the direct bonding of cyanide to the FeMo-cofactor. These data indicate that both acetylene and cyanide are able to interact with FeMo-cofactor contained within the alpha-96-substituted MoFe proteins in the resting state. These results support a model where effective interaction of substrates or inhibitors with FeMo-cofactor occurs as a consequence of both increased reactivity and accessibility of FeMo-cofactor under turnover conditions. We suggest that, for the wild-type MoFe protein, the alpha-96(Arg) side chain acts as a gatekeeper, moving during turnover in order to permit accessibility of acetylene or cyanide to a specific [4Fe-4S] face of FeMo-cofactor.

Acetylene↗
PubMed2003

Structure-based mutagenesis of the malonyl-CoA:acyl carrier protein transacylase from Streptomyces coelicolor.

Malonyl-CoA:acyl carrier protein transacylase (MAT) provides acyl-ACP thioesters for the biosynthesis of aromatic polyketides, and thus is the primary gatekeeper of substrate specificity in type II PKS. A recent report described the X-ray crystal structure of the Streptomyces coelicolor MAT and suggested active site residues which may be important for substrate selectivity [Keatinge-Clay, A. T., et al. (2003) Structure 11, 147-154]. Mutants were made to test the proposed roles of these residues, and the enzymes were characterized kinetically with respect to native and non-native substrates. The activity of the MAT was observed to be greatly attenuated in many of the observed mutants; however, the K(m) for malonyl-CoA was only modestly affected. Our results suggest the MAT uses an active site that is rigorously ordered around the acyl-thioester moiety of the acyl-CoA to facilitate rapid and efficient transacylation to an ACP. Our results also suggest that the MAT does not discriminate against alpha-substituted acyl-CoA thioesters solely on the basis of substrate size.

Acyl-Carrier Protein S-Malonyltransferase↗
PubMed2004

Elimination of a misfolded folding intermediate by a single point mutation.

We present an analysis of the folding behavior of the 159-residue major birch pollen allergen Bet v 1. The protein contains a water-filled channel running through it. Consequently, the protein has a hydrophobic shell, rather than a hydrophobic core. During the folding of the protein from either the urea-, pH-, or SDS-denatured state, Bet v 1 transiently populates a partially folded intermediate state. This state appears to be misfolded, since it has to unfold at least partially to fold to the native state. The misfolded intermediate is not, however, a result of the water-filled channel in Bet v 1. The intermediate completely disappears in the mutant Tyr --> Trp120, in which the channel is still present. Tyr120 appears to behave as a "negative gatekeeper" which attenuates efficient folding. The close structural homologue, the apple allergen Mal d 1, also folds without any detectable folding intermediates. However, the position of the transition state on the reaction coordinate, which is a measure of its overall compactness relative to the denatured and native states, is reduced dramatically from ca. 0.9 in Bet v 1 to around 0.5 in Mal d 1. We suggest that this large shift in the transition state structure is partly due to different local helix propensities. Given that individual mutations can have such large effects on folding, one should not a priori expect structurally homologous proteins to fold by the same mechanism.

Allergens↗
PubMed2005

Kinetics of iron release from ferric binding protein (FbpA): mechanistic implications in bacterial periplasm-to-cytosol Fe3+ transport.

The ferric binding protein (FbpA) transports iron across the periplasmic space of certain Gram-negative bacteria and is an important component involved in iron acquisition by pathogenic Neisseria spp. (Neisseria gonorrheae and Neisseria meningitidis). Previous work has demonstrated that the synergistic anion, required for tight Fe(3+) sequestration by FbpA, also plays a key role in inserting Fe(3+) into the FbpA binding site. Here, we investigate the iron release process from various forms of holo-FbpA, Fe(3+)FbpA-X, during the course of a chelator competition reaction using EDTA and Tiron. Fe(3+)FbpA-X represents the protein assembly complex with different synergistic anions, X = PO(4)(3)(-) and NTA. Stepwise mechanisms of Fe(3+) release are proposed on the basis of kinetic profiles of these chelator competition reactions. Fe(3+)FbpA-PO(4) and Fe(3+)FbpA-NTA react differently with EDTA and Tiron during the Fe(3+)-exchange process. EDTA replaces PO(4)(3)(-) and NTA from the first coordination shell of Fe(3+) and acts as a synergistic anion to give a spectroscopically distinguishable intermediate, Fe(3+)FbpA-EDTA, prior to pulling Fe(3+) out of the protein. Tiron, on the other hand, does not act as a synergistic anion but is a more efficient competing chelator as it removes Fe(3+) from FbpA at rate much faster than EDTA. These results reaffirm the contribution of the synergistic anion to the FbpA iron transport process as the anion, in addition to playing a facilitative role in iron binding, appears to have a "gatekeeper" role, thereby modulating the Fe(3+) release process.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗
PubMed2005

Conformational dynamics of M2 helices in KirBac channels: helix flexibility in relation to gating via molecular dynamics simulations.

KirBac1.1 and 3.1 are bacterial homologues of mammalian inward rectifier K channels. We have performed extended molecular dynamics simulations (five simulations, each of >20 ns duration) of the transmembrane domain of KirBac in two membrane environments, a palmitoyl oleoyl phosphatidylcholine bilayer and an octane slab. Analysis of these simulations has focused on the conformational dynamics of the pore-lining M2 helices, which form the cytoplasmic hydrophobic gate of the channel. Principal components analysis reveals bending of M2, with a molecular hinge at the conserved glycine (Gly134 in KirBac1.1, Gly120 in KirBac3.1). More detailed analysis reveals a dimer-of-dimers type motion. The first two eigenvectors describing the motions of M2 correspond to helix kink and swivel motions. The conformational flexibility of M2 seen in these simulations correlates with differences in M2 conformation between that seen in the X-ray structures of closed channels (KcsA and KirBac) in which the helix is undistorted, and in open channels (e.g. MthK) in which the M2 helix is kinked. Thus, the simulations, albeit on a time scale substantially shorter than that required for channel gating, suggest a gating model in which the intrinsic flexibility of M2 about a molecular hinge is coupled to conformational transitions of an intracellular 'gatekeeper' domain, the latter changing conformation in response to ligand binding.

Animals↗
PubMed2005

Establishing the principles of recognition in the adenine-binding region of an aminoglycoside antibiotic kinase [APH(3')-IIIa].

The protein-based molecular recognition of the adenine ring has implications throughout biological systems. In this paper, we discuss the adenine-binding region of an aminoglycoside antibiotic kinase [APH(3')-IIIa], which serves as an excellent model system for proteins that bind the adenine ring. This enzyme employs a hydrogen-bonding network involving water molecules along with enzyme backbone/side-chain atoms and a pi-pi stacking interaction to recognize the adenine ring. Our approach utilized site-directed mutagenesis, adenosine analogues and a variety of biophysical methods to probe the contacts in the adenine-binding region of APH(3')-IIIa. The results point to the polar nature of an adenine-Met90 contact in this binding pocket and the important role that Met90, the "gatekeeper" residue in structurally similar Ser/Thr protein kinases, plays in adenine binding. The results also suggest that small changes in the structure of the adenine ring can lead to significant changes in the ability of these analogues to occupy the adenine-binding region of the enzyme. Additional computational experiments indicate that both size and electronic factors are important in the binding of aromatic systems in this interaction-rich pocket. The principles governing adenine recognition established in this study may be applied to other protein-ligand complexes and used to navigate future studies directed at discovering potent and selective inhibitors of APH-type enzymes.

Adenine↗
PubMed2006

Reaction geometry and thermostable variant of pyranose 2-oxidase from the white-rot fungus Peniophora sp.

Pyranose 2-oxidase catalyzes the oxidation of a number of carbohydrates using dioxygen; glucose, for example, is oxidized at carbon 2. The structure of pyranose 2-oxidase with the reaction product 2-keto-beta-d-glucose bound in the active center is reported in a new crystal form at 1.41 A resolution. The binding structure suggests that the alpha-anomer cannot be processed. The binding mode of the oxidized product was used to model other sugars accepted by the enzyme and to explain its specificity and catalytic rates. The reported structure at pH 6.0 shows a drastic conformational change in the loop of residues 454-461 (loop 454-461) at the active center compared to that of a closely homologous enzyme analyzed at pH 4.5 with a bound acetate inhibitor. In our structures, the loop is highly mobile and shifts to make way for the sugar to pass into the active center. Presumably, loop 454-461 functions as a gatekeeper. Apart from the wild-type enzyme, a thermostable variant was analyzed at 1.84 A resolution. In this variant, Glu542 is exchanged for a lysine. The observed stabilization could be a result of the mutated residue changing an ionic contact at a comparatively weak interface of the tetramer.

Basidiomycota↗
PubMed1997

Quantitative kinetic model for photoassembly of the photosynthetic water oxidase from its inorganic constituents: requirements for manganese and calcium in the kinetically resolved steps,.

The process of photoactivation, the assembly of a functional water-oxidizing complex (WOC) from the apoproteins of photosystem II of higher plants and inorganic cofactors (Mn2+, Ca2+, and Cl-), was known from earlier works to be a two-step kinetic process, requiring two light-induced processes separated by a slower dark period. However, these steps had not been directly resolved in any kinetic experiment, until development of an ultrasensitive polarographic O2 electrode and synthesis of an improved chelator for cofactor removal allowed direct kinetic resolution of the first pre-steady state intermediate [Ananyev, G. M. & Dismukes, G. C. (1996a) Biochemistry 35, 4102-4109]. Herein, the dependence of the rates of each of the first two light steps and the dark step of photoactivation was directly determined in spinach PSII membranes over a range of calcium and manganese concentrations at least 10-fold lower than those possible using commercial O2 electrodes. The following results were obtained. (1) One Mn2+ ion binds and is photooxidized to Mn3+ at a high-affinity site, forming the first light-induced intermediate, IM1. Formation of IM1 is coupled to the dissociation of a bound Ca2+ ion either located in the Mn site or coupled to it. (2) The inhibition constant for Ca2+ dissociation from this site is equal to 1.5 mM. (3) The dissociation constant of Mn2+ at this high-affinity site is equal to 8 microM at the optimum calcium concentration for O2-evolving activity of 8 mM, in agreement with the high-affinity site for electron donation to PSII. (4) Prior to the next photolytic step, one Ca2+ ion must bind at its effector site so that stable photooxidation of a second Mn2+ ion can occur, forming the second light-induced intermediate, IM2. This dark process is the rate-determining step. (5) The Michaelis constant for recovery of O2 evolution by Ca2+ binding at this effector site (Km) is equal to 1.4 mM, a value that is the same as that measured for the calcium requirement for O2 evolution in intact PSII. (6) The low quantum yield for the formation of IM2 from IM1 increases linearly with the duration of the dark period up to the longest period we could examine (10 s). Accordingly, the rate limitation in the second photolytic step originates from a slow calcium-induced dark rearrangement of the first intermediate, IM1, which we propose to be a protein conformational change that allows stable binding of the next Mn2+ ion. We further propose that the single Ca2+ ion which is required for assembly of the Mn4 cluster is equivalent to the Ca2+ ion which functions at the "gatekeeper" site in intact O2-evolving centers, where it plays a role in limiting substrate access to the Mn4 cluster [Sivaraja, M., et al. (1989) Biochemistry 28, 9459-9464; Tso, J., et al., (1991) Biochemistry 30, 4734-4739]. A molecular model for photoactivation is proposed and discussed.

Calcium↗
PubMed1999

Metabolic fate of oxidized guanine ribonucleotides in mammalian cells.

8-Oxo-7,8-dihydroguanine- (8-oxoguanine-) containing nucleotides are generated in the cellular nucleotide pool by the action of oxygen radicals produced during normal cellular metabolism. We examined the interconversion and metabolic fate of 8-oxoguanine-containing ribonucleotides in mammalian cells. (1) 8-OxoGTP can be generated not only by direct oxidation of GTP but also by phosphorylation of 8-oxoGDP by nucleotide diphosphate kinase, and the 8-oxoGTP thus formed can serve as a substrate for RNA polymerase II to induce transcription errors. (2) MTH1 protein carrying intrinsic 8-oxo-dGTPase activity has the potential to hydrolyze 8-oxoGTP to 8-oxoGMP, thus preventing misincorporation of 8-oxoguanine into RNA. 8-OxoGMP, the degradation product, cannot be reutilized, since guanylate kinase, which has the potential to phosphorylate both GMP and dGMP, is inactive on 8-oxoGMP. (3) Ribonucleotide reductase, which catalyzes reduction of four naturally occurring ribonucleoside diphosphates, cannot convert 8-oxoguanine-containing ribonucleotide to the deoxyribonucleotide. This step appears to serve as a gatekeeper to prevent formation of mutagenic substrates for DNA synthesis from oxidized ribonucleotides.

Animals↗