THERMAL DENATURATION OF MONOMERIC AND TRIMERIC PHYCOCYANINS STUDIED BY STATIC AND SPECTROSCOPY POLARIZED TIME-RESOLVED FLUORESCENCE

C-Phycocyanin (PC) and allophycocyanin (APC). as well as the a-subunit of PC. have been isolated from the blue-green alga (cyanobacterium). Spirulina platensis. The effects of partial thermal denaturation of PC and of its state of aggregation have been studied by ps time-resolved, polarized fluorescence spectroscopy. All measurements have been performed under low photon fluxes (< 10’ ’ photonsipulse x cm’) to minimize singlet-singlet annihilation processes. A complex decay is obtained under most conditions, which can be fitted satisfactorily with a bi-exponential (7’ = 70400 ps. T? = 1000-3000 ps) for both the isotropic and the polarized part, but with different intensities and time constants for the two decay curves. The data are interpreted in the frameworkof the model first developed by Teak and Dale (Biochern. J. 116, 161 (1970)], which divides the spectroscopically different chromophores in (predominantly) sensitizing (s) and fluorescing U, ones. If one assumes temperature dependent losses in the energy transfer from the s to the f and between f chromophores. both the biexponential nature of the isotropic fluorescence decay and the polarization data can be rationalized. In the isotropic emission (corresponding to the population of excited states) the short lifetime is related to the s-,f transfer. the longer one to the “free“ decay of the final acceptor(s) (= f). The polarized part is dominated by an extremely short decay time. which is related to s+f transfer, as well as to resonance transfer between the f-chromophores

PHOTOCHEMISTRY OF PHYCOBILIPROTEINS

Native PEC from the cyanobacterium, Mastigocladus laminosus, and its isolated α-subunit show photoreversibly photochromic reactions with difference-maxima around 502 and 570 nm in the spectral region of the α-84 phycoviolobilin chromophore. (b) Native PEC and its β-subunit show little if any reversible photochemistry in the 600–620 nm region, where the phycocyanobilin chromophores on the β-subunit absorb maximally, (c) Reversible photochemistry is retained in ureadenatured PEC at pH = 7.0 or pH ≤ 3. The difference maxima are shifted to 510 and 600 nm, and the amplitudes are decreased. An irreversible absorbance increase occurs around 670 nm (pH ≤ 3). (d) The amplitude of the reversible photoreaction difference spectrum is maximum in the presence of 4–5 M urea or 1 M KSCN, conditions known to dissociate phycobiliprotein aggregates into monomers. At the same time, the phycocyanobilin chromophore(s) are bleached irreversibly, (e) The amplitude becomes very small in high aggregates, e.g. in phycobilisomes. (f) In a reciprocal manner, the phototransformation of native PEC leads to a reversible shift of its aggregation equilibrium between trimer and monomer. The latter is favored by orange, the former by green light, (g) It is concluded that the phycoviolobilin chromophore of PEC is responsible for reversible photochemistry in PEC, and that there is not only an influence of aggregation state on photochemistry, but also vice versa an effect of the status of the chromophore on aggregation state. This could constitute a primary signal in the putative function as sensory pigment, either directly, or indirectly via the release of other polypeptides, via photodynamic effects, or the like

The Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory is a second generation water Cherenkov detector designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The detector is unique in its use of D2O as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates. In this paper the physical properties, construction, and preliminary operation of the Sudbury Neutrino Observatory are described. Data and predicted operating parameters are provided whenever possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and epsf style files. For additional information about SNO see http://www.sno.phy.queensu.ca . This version has some new reference

Low diagnostic value of respiratory impedance measurements in children

The aim of this study was to determine whether impedance values in children with various chronic respiratory complaints differed from those observed in symptom-free children. Respiratory impedance was measured using the forced oscillation technique in 1,776 Dutch children aged 6-12 yrs. In addition to the commonly used parameters of resistance and reactance, further impedance parameters were obtained by using linear and quadratic regression to describe individual resistance and reactance curves as a function of frequency. Furthermore, the diagnostic value of the individual impedance parameters was evaluated by means of receiver operator characteristic (ROC) curves. Statistically significant differences in impedance values were found in girls with symptoms suggesting asthma compared to symptom-free girls, but not in boys. In children with chronic cough, impedance was not significantly different from the values of symptom-free children. The results obtained by the additional impedance parameters were comparable to those of the commonly used measures. We conclude that the diagnostic value of the impedance parameters appeared to be low, as no cut-off points were found to discriminate clearly between symptomatic and symptom-free children. These findings may reflect absence of functional abnormalities in symptomatic children at this age. (C)ERS Journals Ltd 1997

Childhood social class and cancer incidence: results of the globe study

Despite increased recognition of the importance of investigating socio-economic inequalities in health from a life course perspective, little is known about the influence of previous termchildhoodnext term socio-economic position (SEP) on previous termcancer incidence.next term The authors studied the association between father's occupation and adult previous termcancer incidencenext term by linking information from the longitudinal GLOBE study with the regional population-based Eindhoven previous termCancernext term Registry (the Netherlands) over a period of 14 years. In 1991, 18,973 participants (response rate 70.1%) of this study responded to a postal questionnaire, including questions on SEP in youth and adulthood. Respondents above the age of 24 were included (N = 12,978). Cox regression was used to calculate hazard ratios (HR) for all previous termcancersnext term as well as for the five most frequently occurring previous termcancersnext term by respondent's educational level or occupational previous termclass,next term and by father's occupational previous termclassnext term (adjusted for respondent's education and occupation). Respondents with a low educational level showed an increased risk of all previous termcancers,next term lung and breast previous termcancernext term (in women). Respondents with a low adult occupational level showed an increased risk of lung previous termcancernext term and a reduced risk of basal cell carcinoma. After adjustment for adult education and occupation, respondents whose father was in a lower occupational previous termclassnext term showed an increased risk of colorectal previous termcancernext term as compared to those with a father in the highest previous termsocial class.next term In contrast, respondents whose father was in a lower occupational previous termclass,next term showed a decreased risk of basal cell carcinoma as compared to those with a father in the highest occupational previous termclass.next term The association between previous termchildhoodnext term SEP and previous termcancer incidencenext term is less consistent than the association between adult SEP and previous termcancer incidence,next term but may exist for colorectal previous termcancernext term and basal cell carcinoma

Object-based change detection using correlation image analysis and image segmentation

This study introduces change detection based on object/neighbourhood correlation image analysis and image segmentation techniques. The correlation image analysis is based on the fact that pairs of brightness values from the same geographic area (e.g. an object) between bi-temporal image datasets tend to be highly correlated when little change occurres, and uncorrelated when change occurs. Five different change detection methods were investigated to determine how new contextual features could improve change classification results, and if an object-based approach could improve change classification when compared with per-pixel analysis. The five methods examined include (1) object-based change classification incorporating object correlation images (OCIs), (2) object-based change classification incorporating neighbourhood correlation images (NCIs), (3) object-based change classification without contextual features, (4) per-pixel change classification incorporating NCIs, and (5) traditional per-pixel change classification using only bi-temporal image data. Two different classification algorithms (i.e. a machine-learning decision tree and nearest-neighbour) were also investigated. Comparison between the OCI and the NCI variables was evaluated. Object-based change classifications incorporating the OCIs or the NCIs produced more accurate change detection classes (Kappa approximated 90%) than other change detection results (Kappa ranged from 80 to 85%).close10510

Identification of an SCF ubiquitin-ligase complex required for auxin response in Arabidopsis thaliana

NRC publication: Ye