The correlation of RNase A enzymatic activity with the changes in the distance between Nepsilon2-His12 and N delta1-His119 upon addition of stabilizing and destabilizing salts.

The effect of stabilizing and destabilizing salts on the catalytic behavior of ribonuclease A (RNase A) was investigated at pH 7.5 and 25 degrees C, using spectrophotometric, viscometric and molecular dynamic methods. The changes in the distance between N(epsilon2) of His(12) and N(delta1) of His(119) at the catalytic center of RNase A upon the addition of sodium sulfate, sodium hydrogen sulfate and sodium thiocyanate were evaluated by molecular dynamic methods. The compactness and expansion in terms of Stokes radius of RNase A upon the addition of sulfate ions as kosmotropic salts, and thiocyanate ion as a chaotropic salt, were estimated by viscometric measurements. Enzyme activity was measured using cytidine 2', 3'-cyclic monophosphate as a substrate. The results from the measurements of distances between N(epsilon2) of His(12) and N(delta1) of His(119) and Stokes radius suggest (i) that the presence of sulfate ions decreases the distance between the catalytic His residues and increases the globular compactness, and (ii) that there is an expansion of the enzyme surface as well as elongation of the catalytic center in the presence of thiocyanate ion. These findings are in agreement with activity measurements

Galaxies at a redshift of similar to 0.5 around three closely spaced quasar sightlines

We examine the relationship between galaxies and the intergalactic medium at z < 1 using a group of three closely spaced background quasi-stellar objects (QSOs) with zem ≈ 1 observed with the Hubble Space Telescope. Using a new grouping algorithm, we identify groups of galaxies and absorbers across the three QSO sightlines that may be physically linked. There is an excess number of such groups compared to the number we expect from a random distribution of absorbers at a confidence level of 99.9 per cent. The same search is performed with mock spectra generated using a hydrodynamical simulation, and we find that the vast majority of such groups arise in dense regions of the simulation.We find that atz<0.5, groups in the simulation generally trace the large-scale filamentary structure as seen in the projected 2D distribution of the HI column density in an ∼30 h −1 Mpc region. We discover a probable sub-damped Lyman α system at z = 0.557 showing strong, low-ionization metal absorption lines. Previous analyses of absorption across the three sightlines attributed these metal lines to HI. We show that even when the new line identifications are taken into account, evidence remains for planar structures with scales of ∼1 Mpc absorbing across the three sightlines. We identify a galaxy at z = 0.2272 with associated metal absorption in two sightlines, each 200 kpc away. By constraining the star formation history of the galaxy, we show that the gas causing this metal absorption may have been enriched and ejected by the galaxy during a burst of star formation 2 Gyr ago