Comparative modelling of tetramanganese cluster of Chaetosphaeridium globosum.

The DI protein of photosystem II (PS II) complex of a microalga Chaetosphaeridium globosum has been theoretically modelled from its sequence using comparative modeling with known backbone structure of DI protein from bacterium Thermosynechococcus vulcanus as template. The model is built with missing loops and all side chains, which are not resolved in the structure of the template. The structure of the tetramanganese cluster (TMC) and the ligand forming side chains have been subjected to modeling studies in order to gather more information useful to understanding of the water splitting reactions. Earlier models of TMC have been scrutinized and an insight into the manganese coordination sphere has been provided.

A model for the organization of chlorophyll-protein complex of photosystem II and analysis of its photochemical efficiency and excitation migration.

A model is proposed for the organization of chlorophyll-protein complex in photosystem II (PS II) of higher plants. The rates of exciton migration and exciton trapping have been computed using stochastic method to find out the photochemical efficiency of the dimeric PS II. Three dimeric PS II units are assumed to form a group, as transfer of the exciton to the light harvesting bed of the nearest neighbour on either side may only be effective. A relationship has been deduced between the fractions of the reaction centre traps closed and the number of jumps (J) required by the exciton for trapping. The photochemical efficiency and fluorescence quantum yield are computed using J as the parameter in an empirical equation.

Modelling a binuclear metal binding site in the photosynthetic reaction centre II.

Based on the experimental data and homologous sites in Protein Data Bank (PDB) a model for metal binding sites in D1/D2 heterodimer has been proposed. On searching for tetranuclear and binuclear Mn binding sites in the PDB, a suitable sequence homology in thermolysin and D1 could be observed. From the homology and site-directed mutagenesis data, a model for binuclear Mn-Ca or Mn-Mn has been built and it is extended to a tetranuclear Mn centre.

Inhalation of amyl nitrite and the measurement of left ventricular outflow velocity: studies in normal, young adults.

Amyl nitrite inhalation is useful in the identification of patients with provocable left ventricular (LV) outflow tract obstruction. However, there are no prospective studies that assess the normal change in LV outflow velocity during this intervention. Eighteen normal subjects (mean age, 34+/-5 years; 9 men and 9 women) inhaled amyl nitrite during measurement of LV outflow velocity. Peak velocity increased from 109+/-16 cm/s to 144+/-24 cm/s (P<0.001). There were no significant gender differences in velocity measurements at baseline or at peak. Our study provides prospective data that may be useful when evaluating young adults for LV outflow tract obstruction with Doppler echocardiography during amyl nitrite inhalation.

Prediction of structure of antenna proteins of photosystem II.

Membrane spanning regions of 43 kDa and 47 kDa antenna proteins of photosystem II of thylakoid membranes are theoretically predicted. Prediction of topology of chlorophyll-a and beta-carotene molecules in the proteins and interaction of the proteins with 33 kDa extrinsic protein on the lumenal side of thylakoid membrane is based on the findings reported earlier. Each antenna protein is predicted to have six transmembrane alpha-helices with twelve chlorophyll-a and five beta-carotene molecules binding to it. Both N- and C- terminal ends are proposed to be on the stromal side of thylakoid membrane. The proposed structural model conforms to the reported experimental results from the literature.

Prediction of structure and organisation of chlorophyll a/b binding polypeptides in PS I and II.

Secondary structures, functionally important residues, antigenic sites, membrane spanning segments and hydropathicity of light harvesting chlorophyll a/b binding polypeptides (LHC) are predicted by theoretical methods from the amino acid sequence of the polypeptides. The reported structural features of the Pea LHC (Lhcb 1 gene product) from electron crystallographic studies have been compared by alignment with other types of chlorophyll a/b binding polypeptides for structural prediction. Fifteen conserved residues D85, D89, E113, H116, E/Q133, E/Q181, E189, D/N233, E252, N/H255, Q/E269, E/D/Q280, N281, H285, D288 (number indicates position in the aligned sequence), are identified which are potential ligands to Mg2+ of chlorophylls. Three amino acid residues D89, E/Q131 and D/N 233 are proposed as ligands to chlorophylls b2, a7 and b2 respectively, for which ligands are not identified in electron crystallographic study.

Estimation of left ventricular cavity area with an on-line, semiautomated echocardiographic edge detection system.

BACKGROUND: Automated edge detection of endocardial borders in echocardiograms provides objective, reproducible estimation of cavity area; however, most methods have required off-line analysis. A recently developed prototype echocardiographic imaging system permits real-time automated edge detection during imaging and thus, the potential for measurement of cyclic changes in cavity area and the assessment of left ventricular function on-line. Our purpose was to compare measurements of endocardial area manually traced from conventional echocardiograms with those obtained with the real-time automated edge detection system in normal subjects. METHODS AND RESULTS: Two training sets of images were used to establish optimal methods of gain setting; the settings were then evaluated in a test set of images. In the high-gain training group (n = 8 subjects, 119 images), gain settings were adjusted sufficiently high to display at least 90% of the endocardial border. Manually drawn and real-time area measurements correlated at r = 0.92, but manually drawn areas were underestimated by computer. In the low-gain training group (n = 7 subjects, 104 images), gain settings were adjusted sufficiently low to avoid cavity clutter despite the presence of dropout of endocardial edges. Manually drawn and real-time areas again correlated (r = 0.79), but manually drawn areas were overestimated by computer. In the intermediate-gain test group (n = 7 subjects, 105 images), gain settings were balanced between maximal endocardial definition (greater than or equal to 90%) and minimal cavity clutter (less than or equal to 1 cm2). Manually drawn and real-time areas correlated at r = 0.91 for the group, and r ranged from 0.94 to 0.99 in individual subjects. Interobserver variability was 9.5% for manually traced areas and 10.6% for real-time area measurements. CONCLUSIONS: Real-time on-line automated edge detection provides accurate estimation of manually drawn cavity areas. Although the method is gain dependent, measurements are reproducible. The system should have clinical application in settings in which measurements of left ventricular function are important.