The stable tyrosyl radical in photosystem II: why D?

Two redox-active tyrosines are present in Photosysytem II, the water-oxidizing enzyme. While the tyrosine that is kinetically competent in electron transfer, TyrZ, may also have a role in the enzyme mechanism, the second tyrosine, TyrD, has a stable radical and is not directly involved in the redox chemistry associated with enzyme function. Nevertheless, reasonable mechanistic roles for TyrD have been postulated that satisfy desires to rationalise the presence of this cofactor, or, in English, we think we know what it does. First, the TyrD radical acts an oxidant of the Mn cluster in the lowest state of the redox accumulation cycle (i.e., S(0)), providing potential benefits in maintaining the cluster in the more stable higher valence states. This redox role may also be important during Mn assembly and indeed overreduced forms of the Mn cluster appear to be oxidised by TyrD(*). Second, the proton generated by the TyrD radical is thought to remain in its vicinity having an electrostatic influence on the location and potential of the chlorophyll cation, P(+). This effect may be important for the kinetics of TyrZ oxidation and may provide a significant thermodynamic boost to the enzyme. In addition, through its electrostatic influence, TyrD(*)(H(+)) may confine the highly oxidising cation P(+) to the chlorophyll nearest to TyrZ, thereby accelerating TyrZ oxidation and restricting the potentially damaging redox chemistry to one side of the reaction centre: the disposable D1 side. This second role, evidence for which is beginning to emerge, constitutes a new role for a redox-active tyrosine in biology: as a positive charge generator in a hydrophobic environment. In this short review, we focus on work relevant to these two roles.     

Laparoscopic radical prostatectomy in obese patients: feasible or foolhardy?

More than 70% of men who are candidates for radical prostatectomy can be classified as either overweight or obese by body mass index. The role for laparoscopic radical prostatectomy (LRP) in treating these patients remains to be defined. A wealth of experience from bariatric surgery confirms that laparoscopic procedures can be performed successfully, even in the setting of morbid obesity, despite well-defined derangements in respiratory dynamics. Using the technical modifications outlined here, LRP can be performed safely and effectively in obese patients. Obesity raises the degree of difficulty for LRP, however, resulting in longer operative times and possibly a higher rate of open conversion. For this reason, surgeons early in their LRP experience are advised to avoid obese patients until they have become facile in the performance of LRP in normal-weight individuals.     

Asymmetrical radical formation in D- and L-alanines irradiated with tritium-β-rays

Radical formation in D- and L-alanines was studied using ESR after internal³H--irradiation under the situation in which the contribution of Bremsstrahlung to form the radicals is assumed to be considerably less than the case of^{9 0}Y--irradiation. It was demonstrated that the relative radical concentration by the -rays was distinguishably higher in D-alanine than in L-alanine. Thus the asymmetry found in these experiments in the radical formation of the alanines may be attributed to the different interaction between the polarized electrons and the two enantiomers.     

Asymmetrical radical formation in D- and L-alanines irradiated with yttrium-90β-rays

Radical formation in^{9 0}Y--irradiated D- and L-alanines was studied using ESR. It was observed that the relative radical concentration by -irradiation was distinguishably (13.9–21.5%) more in D-alanine than in L-alanine. Discussion was made on the possible mechanisms for the observed results.     

Human NADH:ubiquinone oxidoreductase deficiency: radical changes in mitochondrial morphology?

Malfunction of NADH:ubiquinone oxidoreductase or complex I (CI), the first and largest complex of the mitochondrial oxidative phosphorylation system, has been implicated in a wide variety of human disorders. To demonstrate a quantitative relationship between CI amount and activity and mitochondrial shape and cellular reactive oxygen species (ROS) levels, we recently combined native electrophoresis and confocal and video microscopy of dermal fibroblasts of healthy control subjects and children with isolated CI deficiency. Individual mitochondria appeared fragmented and/or less branched in patient fibroblasts with a severely reduced CI amount and activity (class I), whereas patient cells in which these latter parameters were only moderately reduced displayed a normal mitochondrial morphology (class II). Moreover, cellular ROS levels were significantly more increased in class I compared with class II cells. We propose a mechanism in which a mutation-induced decrease in the cellular amount and activity of CI leads to enhanced ROS levels, which, in turn, induce mitochondrial fragmentation when not appropriately counterbalanced by the cell's antioxidant defense systems.     

Is there evidence for excessive free radical production in vivo during ultrasound-assisted liposuction?

The surgical technique of ultrasound-assisted liposuction has become a standard procedure for the treatment of lipodystrophy. However, little is known about the impact of this therapy on fatty tissue on the molecular level. There are concerns about possible adverse effects related to the high-intensity ultrasound energy, because in vitro studies have shown a substantial generation of free radicals. In this study, the authors investigated whether ultrasound waves can create an excessive free radical production in vivo by measuring lipid peroxidation products in the form of malondialdehyde equivalents. For this purpose, the thiobarbituric acid-reactive substances (TBARS) assay was chosen. In this test, malondialdehyde, a major product of lipid peroxidation, reacts with thiobarbituric acid to produce a pink adduct that can be measured spectrophotometrically. The authors determined oxidation products in 28 aspirates of 17 treated patients before ultrasound-assisted liposuction (0 minutes) to establish a baseline concentration and at 2, 5, and 10 minutes after the treatment was begun. Median malondialdehyde concentration of the control group (conventional liposuction, 0 minutes) was 3.40 nmol of malondialdehyde per gram of adipose tissue. Median concentrations after 2, 5, and 10 minutes of ultrasound-assisted liposuction were 7.45 (n = 28), 8.84 (n = 21), and 4.07 (n = 8) nmol malondialdehyde per gram adipose tissue, respectively. The differences were not statistically significant. The data suggest that there is no excessive formation of lipid oxidation products in response to free radicals. The antioxidative capacity of adipose tissue does not seem to be overwhelmed by the standard application regimen of ultrasound-assisted liposuction.     

Mitochondria and aging: innocent bystanders or guilty parties?

There are many theories of aging and a number ofthem encompass the role of mitochondria in this process. Mitochondrial DNA mutations and deletions have been shown to accumulate in many tissues in mammals during aging. However, there is little evidence that these mutations could affect the functioning of aging tissues.     

Monoamine oxidase-induced hydroxyl radical production and cardiomyocyte injury during myocardial ischemia–reperfusion in rats

To elucidate the involvement of monoamine oxidase (MAO) in hydroxyl radical production and cardiomyocyte injury during ischemia as well as after reperfusion, we applied microdialysis technique to the heart of anesthetized rats. Dialysate samples were collected during 30?min of induced ischemia followed by 60?min of reperfusion. We monitored dialysate 3,4-dihydrobenzoic acid (3,4-DHBA) concentration as an index of hydroxyl radical production using a trapping agent (4-hydroxybenzoic acid), and dialysate myoglobin concentration as an index of cardiomyocyte injury in the ischemic region. The effect of local administration of a MAO inhibitor, pargyline, was investigated. Dialysate 3,4-DHBA concentration increased from 1.9?±?0.5?nM at baseline to 3.5?±?0.7?nM at 20–30?min of occlusion. After reperfusion, dialysate 3,4-DHBA concentration further increased reaching a maximum (4.5?±?0.3?nM) at 20–30?min after reperfusion, and stabilized thereafter. Pargyline suppressed the averaged increase in dialysate 3,4-DHBA concentration by ～72% during occlusion and by ～67% during reperfusion. Dialysate myoglobin concentration increased from 235?±?60?ng/ml at baseline to 1309?±?298?ng/ml at 20–30?min after occlusion. After reperfusion, dialysate myoglobin concentration further increased reaching a peak (5833?±?1017?ng/ml) at 10–20?min after reperfusion, and then declined. Pargyline reduced the averaged dialysate myoglobin concentration by ～56% during occlusion and by ～41% during reperfusion. MAO plays a significant role in hydroxyl radical production and cardiomyocyte injury during ischemia as well as after reperfusion.     

Personal commentaryExternal quality assessment (EQA) in gynaecological cytology: radical rethinking required?

Accepted for publication 19 February 1999
THE PAST
The value of EQA in pathology, including proficiency testing in gynaecological cytology, has been the subject of much recent lively debate^1–6. In summary, the proven role of EQA in the monitoring of personal performance and ability is still uncertain. Furthermore, its potential to prevent critical incidents remains purely speculative. Also, whether EQA would be better replaced, for some or all professional groups, by other methods of quality assurance is unknown. Similarly, whether EQA can justify the considerable professional time, effort and expense involved has not been resolved.  

THE PRESENT

Not surprisingly, events at Kent & Canterbury Hospitals abruptly halted much of the debate about the foregoing issues⁷. Indeed, as a direct consequence of this and other incidents, the NHS Executive stipulated unilaterally that EQA is now mandatory within the NHS Cervical Screening Programme (CSP)⁸ and reinforced the necessity for all qualified laboratory staff to participate^8–10. A surprise, however, was the Executive's enlightened comments on EQA. First, and of greatest significance, that the principal function of EQA in pathology is to improve standards and advance quality through personal education. Second, that EQA should be seen to complement other QA systems for the early identification of potential problems which might affect patient care. Third, that the identification of individual poor performance through EQA will be exceptional and in essence is a by-product of the basic educational exercise. The latter conclusion was drawn, as far as one can judge, from previous experience with the NHS Breast Screening Programme (NHSBSP) EQA.  

THE FUTURE—PERSONAL SUGGESTIONS FOR OPEN DEBATE

     

Free radical generation induces epithelial-to-mesenchymal transition in lung epithelium via a TGF-β1-dependent mechanism

Fibrotic remodelling of lung parenchymal and airway compartments is the major contributor to life-threatening organ dysfunction in chronic lung diseases such as idiopathic pulmonary fibrosis (IPF) and Chronic Obstructive Pulmonary Disease (COPD). Since transforming growth factor-β1 (TGF-β1) is believed to play a key role in disease pathogenesis and markers of oxidative stress are also commonly detected in bronchoalveolar lavage (BAL) from such patients we sought to investigate whether both factors might be interrelated. Here we investigated the hypothesis that oxidative stress to the lung epithelium promotes fibrotic repair by driving epithelial-to-mesenchymal transition (EMT) via the augmentation of TGF-β1. We show that in response to 400μM hydrogen peroxide (H(2)O(2)) A549 cells, used a model for alveolar epithelium, and human primary bronchial epithelial cells (PBECs) undergo EMT displaying morphology changes, decreased expression of epithelial markers (E-cadherin and ZO-1), increased expression of mesenchymal markers (vimentin and α-smooth muscle actin) as well as increased secretion of extracelluar matrix components. The same oxidative stress also promotes expression of TGF-β1. Inhibition of TGF-β1 signalling as well as treatment with antioxidants such as phenyl tert-butylnitrone (PBN) and superoxide dismutase 3 (SOD3) prevent the oxidative stress driven EMT-like changes described above. Interventions also inhibited EMT-like changes. This study identifies a link between oxidative stress, TGF-β1 and EMT in lung epithelium and highlights the potential for antioxidant therapies to limit EMT and its potential contribution to chronic lung disease.     

The Escherichia coli GTPase ObgE modulates hydroxyl radical levels in response to DNA replication fork arrest

Obg proteins are universally conserved GTP-binding proteins that are essential for viability in bacteria. Homologs in different organisms are involved in various cellular processes, including DNA replication. The goal of this study was to analyse the structure-function relationship of Escherichia?coli ObgE with regard to DNA replication in general and sensitivity to stalled replication forks in particular. Defined C-terminal chromosomal deletion mutants of obgE were constructed and tested for sensitivity to the replication inhibitor hydroxyurea. The ObgE C-terminal domain was shown to be dispensable for normal growth of E.?coli. However, a region within this domain is involved in the cellular response to replication fork stress. In addition, a mutant obgE over-expression library was constructed by error-prone PCR and screened for increased hydroxyurea sensitivity. ObgE proteins with substitutions L159Q, G163V, P168V, G216A or R237C, located within distinct domains of ObgE, display dominant-negative effects leading to hydroxyurea hypersensitivity when over-expressed. These effects are abolished in strains with a single deletion of the iron transporter TonB or combined deletions the toxin/antitoxin modules RelBE/MazEF, strains both of which have been shown to be involved in a pathway that stimulates hydroxyl radical formation following hydroxyurea treatment. Moreover, the observed dominant-negative effects are lost in the presence of the hydroxyl radical scavenger thiourea. Together, these results indicate involvement of hydroxyl radical toxicity in ObgE-mediated protection against replication fork stress.     

Transglycosylation of a β-galactosyl radical, in the course of enzymic hydrolysis of lactose, in the presence of selected polyhydroxyalcohols

Sorbitol, xylitol, erythritol and lactitol were used as the acceptors of galactosyl radicals, in the process of transgalactosylation accompanying the hydrolysis of lactose, conducted with -galactosidase (4.0 ml Lactozym 3000 was added to 430 ml 1.45 M lactose with 0.95 M polyhydroxyalcohols). The following concentrations of galactosyl derivatives of polyols were obtained after hydrolysis for 4 h at 40°C: 0.31 M Gal-erythritol, 0.22 M Gal-xylitol, 0.18 M Gal-sorbitol and 0.14 M Gal-lactitol. A quadruple increase of xylitol content in dry matter of a solution (from 11.5% (w/w) to 44.5% (w/w) brought about a 2.3-fold increase of the product content in the solution (15.2% (w/w) of dry matter).     

Peroxynitrous acid--where is the hydroxyl radical?

Peroxynitrite is an inorganic toxin of physiological interest, formed from the diffusion-controlled reaction of superoxide and nitrogen monoxide with a rate constant of (1.6 +/- 0.3) x 10(10) M(-1) s(-1). On the basis of three experiments we conclude that homolysis of the O-O bond in peroxynitrous acid is unlikely: (1) the yield of nitrite from the decomposition of peroxynitrite shows a dependence on the peroxynitrite concentration and is lower than expected for homolysis; (2) the yield of [15N]nitrate from the reaction of [15N]nitrite with peroxynitrous acid predicted by homolysis does not correspond to that found experimentally, and (3) the reaction of peroxynitrous acid with monohydroascorbate does not yield ascorbyl radicals. Activation volumes determined from high-pressure kinetic studies are inconclusive.     

Radical perineal prostatectomy: a more optimal treatment approach than laparoscopic radical prostatectomy in obese patients?

In comparison with laparoscopic radical prostatectomy (LRP), the perineal approach to radical prostatectomy offers specific technical advantages related to obesity and its unique surgical challenges. Radical perineal prostatectomy (RPP) reduces operative time and its associated risk of complication, which may be more pronounced in obese men. It allows for low blood loss, low postoperative use of narcotics for pain, short hospital stays, and requires only 1 small perineal incision. With a proven history of success, RPP presents obese men with an advantageous surgical option.     

Absorption de l'oxyde nitreux par les parties aeriennes du maïs

Resume Il est montré que les parties aériennes des plantules de maïs semblent capables d'absorber l'oxyde nitreux (N₂O) produit lors de la dénitrification. Cette constatation peut s'avèrer importante au cours d'expériences sur la dénitrification conduites en présence de végétaux.     

Raiding parties of male spider monkeys: Insights into human warfare?

Raids into neighboring territories may occur for different reasons, including the increase of foraging and mating opportunities directly or indirectly through the killing of neighboring rivals. Lethal raids have been mainly observed in humans and chimpanzees, with raiding males being reported to search purposefully for neighbors. Here we report on the first cases ever witnessed of raiding parties of male spider monkeys, a species expected to show such a behavioral tendency, given its similarity with humans and chimpanzees in critical socio-ecological characteristics, such as fission-fusion social dynamics and male-male bonding. Despite the high degree of arboreality of spider monkeys, all seven witnessed raids involved the males progressing single file on the ground in unusual silence. This is remarkably similar to the behavior of chimpanzees. The circumstances around the raids suggest that factors such as reduced mating opportunities, number of males relative to that in the neighboring community, and the strength of bonds among males could play a role in the timing of such actions. The raids did not appear to be aimed at finding food, whereas there is some indication that they may directly or indirectly increase reproductive opportunities. Although no killing was observed, we cannot exclude the possibility that spider monkey raids may be aimed at harming rivals if a vulnerable individual were encountered. The similarity of spider monkey raids with those of chimpanzees and humans supports the notion that lethal raiding is a convergent response to similar socio-ecological conditions.