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PubMed1991

Electron transport in cytochromes P-450 by covalent switching.

The mechanism of electron transfer in cytochrome P-450cam is presented in terms of a covalent switching mechanism. We present a model of putidaredoxin built by homology, which helps explain protein-protein interactions. The mechanism is general enough to account for the genetic variations found in the superfamily of cytochromes P-450. The detail should assist in the design of novel P-450 inhibitors and may have wider implications. The sequence analysis supports our protein model, and highlights the role of cystein and aromatic residues in electron-transport mechanisms. Eukaryotic cytochromes P-450 appear to have evolved their own intramolecular tryptophan electron-transfer mediator, unlike prokaryotic P. putida P-450cam, which still relies upon the C-terminal tryptophan of its attendant electron-transport protein, putidaredoxin. On this basis our protein model is capable of rationalizing the transfer of electrons from NADH to the active site of P-450. At the electronic level the covalent switching that transfers pairs of electrons not only provides a plausible mechanism, but may also have ramifications in a wider context.

Animals↗
PubMed1998

Crystallization and preliminary X-ray diffraction studies of the oxygenating subunit of 3,6-diketocamphane monooxygenase from Pseudomonas putida.

The oxygenating constituent of the 3,6-diketocamphane monooxygenase isozyme from Pseudomonas putida NCIMB 10007 has been crystallized under two different conditions. Crystals were initially grown from polyethylene glycol (PEG) 8000 and sodium acetate using the vapour-phase diffusion method. The crystals were of orthorhombic P212121 space group, with cell dimensions a = 55.8, b = 94.5 and c = 163.7 A and diffracted to 2.8 A resolution. More recently, improved crystals, which diffracted beyond 2 A, have been grown from ammonium sulfate. These crystals also belong to the orthorhombic P212121 space group, with cell dimensions of a = 54.6, b = 93.2 and c = 154. 1 A. A full native data set to 2.5 A resolution has been collected from the ammonium sulfate grown crystals.

Bacterial Proteins↗
PubMed2004

A simple formalism on dynamics of proteins on potential energy landscapes.

We present a simple formalism for the dynamics of proteins on a potential energy landscape, using connectedness of configurational domains as an order parameter. This formalism clearly shows that the energy bias required to form a unit correct contact toward the native configuration of a two-state folder, to overcome Levinthal's paradox, is E(bias) congruent with RT ln 2. This result agrees well with earlier studies and indicates that the bias is mainly due to hydrophobic interaction. Further investigations have shown that the landscape funnel could be experimentally mapped onto a two-dimensional space formed by denaturant concentration and the connectedness of configurational domains. The theoretical value of the depth-of-folding funnel in terms of denaturant concentration has been calculated for a model protein (P450cam), which agrees well with the experimental value. Using our model, it is also possible to explain the turnover nature of heat-capacity change upon unfolding of proteins and the existence of enthalpy and entropy convergence temperatures during unfolding without any strict assumptions as proposed in earlier studies.

Camphor 5-Monooxygenase↗
PubMed2005

Evaluation of a sunscreen photoprotective effect by ascorbic acid assessment in human dermis using microdialysis and gas chromatography mass spectrometry.

Ultraviolet irradiation causes adverse effects like sunburn, photosensitivity reactions or immunologic suppression. The aim of this study was to evaluate the photo-protective outcome of a sunscreen cream (SPF8) by the determination of erythema indexes and the assessment of ascorbic acid and its metabolites in human dermis. These substances were used as markers of oxidative effect. Eight healthy female subjects were enrolled in this study. Two abdominal areas were exposed to solar simulated irradiation with three minimal erythema dose, one with SPF8 application and the other site without SPF8 application. Two other areas were used as control, one without SPF8 application and the other site after SPF8 application. Ascorbic acid and its metabolites (dehydroascorbic acid, threonic acid, oxalic acid and xylose) were collected from human dermis by microdialysis and assessed by gas chromatography mass spectrometry. Irradiated site without sunscreen application had significantly demonstrated lower dermis ascorbic acid concentrations and a higher erythema index than the three other sites (P < 0.05). Threonic acid, oxalic acid and xylose dermis concentrations were significantly higher in site III than in the control site I (P < 0.05). The protected-irradiated site did not show erythema formation and there was stability of ascorbic acid dermis concentrations with non-variation in its metabolites. The assessment of ascorbic acid and its metabolites in human dermis could be an efficient tool to demonstrate the oxidative process and consequently to control the efficiency of sunscreen creams against undesirable UV effects.

Adult↗
PubMed2006

Is there life after Buckley's Formocresol? Part I -- a narrative review of alternative interventions and materials.

OBJECTIVES: (1) To present a narrative review of the currently available alternative interventions and materials to formocresol pulpotomy for the management of extensive caries in the primary molar, and (2) to produce a clinical protocol for pulp therapy techniques in the extensively carious primary molar. INTRODUCTION: The International Agency for Research on Cancer has recently classified formaldehyde as carcinogenic to human beings. Since Buckley's Formocresol contains 19% formaldehyde in its full strength and, therefore, 1% in a 20% dilution, a safer alternative should be identified. METHODS: A narrative review of the published literature for primary molar pulp therapy techniques was undertaken following an extensive and appropriate literature search. A specialist group of paediatric dentists was formed to arrive at a consensus and establish an evidence-based protocol for the management of extensively carious primary molar teeth. Part I of this paper explores the currently available alternative interventions and materials to formocresol in the form of a narrative review. The second part of the paper will present the formation of a specialist group to arrive at a consensus and establish an evidence-based protocol for the management of the extensively carious primary molar. CONCLUSIONS: After consideration of a review of extensively searched literature, a protocol and key points document have been developed to assist clinicians in their treatment planning. Further long-term studies with the highest level of evidence (i.e. randomized controlled trials) are required to enable us to identify acceptable alternatives which can replace formocresol.

Aluminum Compounds↗
PubMed1977

Influence of different endodontic methods of treatment upon the process of apical closure of immature pulpless human teeth and the structure of the newly formed calcified tissue in apical opening.

A description is given of the pathohistological structure of the calcified tissue in the apical opening of four extracted immature pulpless human teeth treated by various endodontic methods. It is concluded that in the tooth treated by mortal extirpation there was neither histological healing nor any tendency for further apex formation. In both the tooth where vital extirpation was performed and in one of the teeth treated as apical periodontitis, the apices were formed from conglomerates of different calcified tissues, identical to the tissue which was formed under comparable conditions in experimental dogs. In the fourth human tooth also treated as apical periodontitis after treatment the apical opening closed with irregular dentine tissue. In this study consideration was given to the problem of the origin of the odontoblasts which co-exist with the hard destructive process present in some pulpless teeth. It is concluded that in the case presented in this study the irregular dentine was formed by the same odontoblasts which took part in the process of normal odontogenesis. This fact, should be respected in the course of endodontic treatment of immature pulpless teeth.

Animals↗
PubMed1991

Occurrence and biological function of cytochrome P450 monooxygenases in the actinomycetes.

Many species within the order Actinomycetales contain one or more soluble cytochrome P450 monooxygenases, often substrate-inducible and responsible for a variety of xenobiotic transformations. The individual cytochromes exhibit a relatively broad substrate specificity, and some strains have the capacity to synthesize large amounts of the protein(s) to compensate for low catalytic turnover with some substrates. All three of the Streptomyces cytochromes sequenced to date are exclusive members of one P450 family, CYP105. In several instances, monooxygenase activity arises from induction of a P450 and associated ferredoxin, or of a P450 only, suggesting that some essential electron donor proteins (reductase and ferredoxin) are not co-ordinately regulated with the cytochrome. The overall properties of these systems suggest an adaptive strategy whose twofold purpose is to maintain a competitive advantage via the production of secondary metabolites, and, whenever possible, to utilize unusual growth substrates by introducing metabolites from these reactions into the more substrate-specific primary metabolic pathways.

Actinomyces↗
PubMed1995

Compressibility of the heme pocket of substrate analogue complexes of cytochrome P-450cam-CO. The effect of hydrostatic pressure on the Soret band.

The effect of hydrostatic pressure on the electronic absorption spectrum of the carbon monoxide complex of cytochrome P-450cam (CYP101) in the presence of various substrates was studied. With increasing pressure the wavenumber of the Soret band in the cytochrome P-450-CO complex shifts linearily to lower values (red-shift) and the half-width increases (broadening). The microscopic theory of solvent-solute interaction discussed by Laird and Skinner is used to explain the observed pressure effects. According to this theory, the slope of the red-shift of the Soret band is related to the compressibility of the chromophore environment, that is the heme moiety of the hemoproteins. It was found that the slope of the red-shift and the slope of the broadening of the Soret band for the CO complex in the presence of various substrate analogues increase with the decrease of the initial high-spin content at 0.1 MPa in the oxidized state. Variation of the high-spin content reflects the changes in the number of water molecules and/or changes in the polarity of the heme environment. The higher compressibility of the cytochrome P-450 complexes with the substrate analogues, which induce a lower degree of the high-spin content in the oxidized protein, is explained by the ability of the water molecules in the heme moiety to transmit the pressure effect on the protein structure to the heme chromophore. Therefore, a larger pressure-induced red-shift of the Soret band in the CO complex of cytochrome P-450cam might indicate a higher water content in the heme environment.

Camphor 5-Monooxygenase↗
PubMed2003

Single olfactory sensory neurons simultaneously integrate the components of an odour mixture.

Most odours are complex mixtures. However, the capacities of olfactory sensory neurons (OSNs) to process complex odour stimuli have never been explored in air-breathing vertebrates. To face this issue, the present study compares the electrical responses of single OSNs to two odour molecules, delivered singly and mixed together, in rats in vivo. This work is the first aimed at demonstrating that single OSNs simultaneously integrate several chemical signals and which, furthermore, attempts to describe such processes for the whole concentration range over which single OSNs can work. The results stress that complex interactions occur between components in odour mixtures and that OSN responses to such mixtures are not simply predictable from the responses to their components. Three types of interactions are described. They are termed suppression, hypoadditivity and synergy, in accord with psychophysical terminology. This allows us to draw links between peripheral odour reception and central odour coding. Indeed, events occurring in single OSNs may account for the dominating or even the masking effects of odour molecules in complex mixtures, i.e. for the prevailing action of a minor component in the final qualitative perception of a mixture. We conclude that our observations with binary mixtures anticipate the complexity of processes which may rise at the level of a single OSN in physiological conditions. Following this hypothesis, a natural odour would induce a multi-chemical integration at the level of single OSNs which may result in refining their individual odour-coding properties, leading them to play a crucial role in the final performance of the olfactory system.

Action Potentials↗
PubMed2006

A novel type of cold-sensitive neuron in rat dorsal root ganglia with rapid adaptation to cooling stimuli.

Cold sensing in mammals is heterogeneous and more than one type of receptor molecule is likely to be involved in the transduction process. Most features of innocuous cold receptors have been explained by TRPM8, the cold and menthol receptor, but their fast adaptation to cooling has not yet been reproduced in cellular systems. In this study we have used a newly developed system for applying fast thermal stimuli to dissociated dorsal root ganglia (DRG) neurons from young rats (150-200 g) in primary culture. We describe a novel type of cold-sensitive rat DRG neuron with rapid adaptation to cooling. These cells (4.3% of the total DRG population) do not express either TRPM8 or the other cold-activated TRP channel, TRPA1, and the epithelial sodium channel (ENaC) is not involved in their transduction. Increases in intracellular calcium induced by cooling in rapidly adapting neurons are caused by calcium entry. These neurons express a large and rapidly adapting cold-induced inward current with a time constant of adaptation in the seconds range, and may correspond to the rapidly adapting cold receptors described in vivo.

Adaptation, Physiological↗
PubMed1993

Contact allergy to sunscreen chemicals in photosensitivity dermatitis/actinic reticuloid syndrome (PD/AR) and polymorphic light eruption (PLE).

From 1989-1991, 214 patients (45 PD/AR, 54 PLE, 115 controls) were patch tested to a sunscreen series containing 9 constituents. 16/214 (7.5%) patients reacted to one or more sunscreens, with allergy being significantly more common in PD/AR patients (10/45 versus 2/54 PLE and 4/115 contact dermatitis clinic controls). The benzophenone group of sunscreens (mexenone, oxybenzone) were the most frequent sensitizers, accounting for 8 of the 27 positive patch tests observed. Clinicians should consider contact allergy to sunscreens in PD/AR patients as an explanation for exposed-site dermatitis episodes.

4-Aminobenzoic Acid↗
PubMed2004

Prevention of ultraviolet-induced skin pigmentation.

BACKGROUND/PURPOSE: Exposure to ultraviolet (UV) radiation increases skin pigmentation and usually results in an even darkening of the skin. However, it may also occasionally lead to the development of hyperpigmented lesions due to a local overproduction of pigment. Skin pigmentation is induced both by UVB and UVA rays. METHODS: The in vivo protection by sunscreens against pigmentation was studied using the determination of a level of protection against pigmentation based on the standardized sun protection factor (SPF) test method. The method includes delayed UVB and UVA pigmentations. The level of prevention against pigmentation was determined 7 days after exposure to solar-simulated radiation by visual assessment. It was calculated using the ratio of the minimal pigmenting dose on protected skin to the minimal pigmenting dose on unprotected skin. Broadspectrum UVB/UVA filters, Mexoryl SX and Mexoryl XL, and complete formula were tested. RESULTS: Protection against pigmentation correlates with the concentration of Mexoryl SX. The levels of protection obtained show a synergetic effect of Mexoryl SX when associated with Mexoryl XL. When different products having the same SPF (same protection against erythema) and different levels of UVA protection are compared, only sunscreen products with a high level of UVA protection show a similar level of protection against sunburn and pigmentation. Products with low UVA protection have a lower capacity of preventing induced pigmentation compared with their efficacy against erythema. CONCLUSIONS: These studies have evidenced that SPF determination was not sufficient to account for the efficiency in preventing pigmentation and that UVA protection was an essential part of this prevention.

Adolescent↗