The effect of calcium on the interaction of protein C with thrombin and the elastase fragment of thrombomodulin: Analysis by analytical ultracentrifugation

The effect of Ca\sp{2+} on the activation of protein C by thrombin bound to the elastase fragment of thrombomodulin (e1TM) is complex. The rate of activation increases from 0 at 0 mM Ca\sp{2+} to a maximum at 0.3 mM Ca\sp{2+} and decreases 25-fold upon further addition of Ca\sp{2+} (Kurosawa et al., 1987). The results reported here demonstrate that thrombin, protein C and e1TM form a complex in the absence of Ca\sp{2+} that falls apart with the addition of Ca\sp{2+}. This observation, in conjunction with the above mentioned kinetic studies, suggests that recognition of protein C by thrombin does not require Ca\sp{2+} but that protein C activation requires a Ca\sp{2+}-induced conformational change; probably in protein C. The technique of sedimentation equilibrium is used to examine the effect of Ca\sp{2+} on the interaction of this enzyme complex made up of three proteins. These proteins studied individually do not significantly self-associate. In all experiments, thrombin was either inhibited with a tripeptide chloromethyl ketone inhibitor (CK), or with diisopropylflourophosphate (DFP). Thrombin and e1TM form a strong 1:1 complex that is relatively unperturbed by the addition of Ca\sp{2+}. Thrombin and protein C form two complexes of 1:1 and 1:2 thrombin:protein C stoichiometry as suggested by the association model that fits the data best. The interactions between thrombin and protein C are strongest in 0 mM Ca\sp{2+}, but become much weaker with the addition of Ca\sp{2+}. Thrombin, protein C and e1TM form a single 1:1:1 complex that behaves similarly to the thrombin/protein C mixture upon the addition of Ca\sp{2+}. Studies with the 42 amino acid Gla ($\gamma$-carboxyglutamic acid) domain peptide and Gla-domainless protein C indicate that, at low Ca\sp{2+} concentrations, the interaction of protein C with thrombin and e1TM may be mediated primarily through this Gla domain. The interaction of activated protein C with thrombin alone, and thrombin with e1TM is also examined. Surprisingly, there is little difference in the interaction of activated protein C as compared to protein C. This is true regardless of whether the thrombin inhibitor is CK which may block some of the substrate recognition site, or DFP, which blocks only the catalytic site. As suggested by these results, activated protein C is a good inhibitor of protein C activation

Self Concept of Academic Ability and Reading Proficiency

Brookover and associates (1962, 1964, 1965) have investigated the nature of self-concept and its effects, and relationships, to the academic achievement. Results reported indicate that there is a direct relationship between self-concept and academic achievement

Lateral Pressure of Concrete on Formwork

Engineerin

Waves in fluid filled elastic tubes.

Massachusetts Institute of Technology. Dept. of Mechanical Engineering. Thesis. 1966. Ph.D.Bibliography: leaf 74.Ph.D

The CORALIE survey for southern extra-solar planets IX. A 1.3-day period brown dwarf disguised as a planet

In this article we present the case of HD 41004 AB, a system composed of a K0V star and a 3.7-magnitude fainter M-dwarf companion separated by only 0.5 arcsec. An analysis of CORALIE radial-velocity measurements has revealed a variation with an amplitude of about 50m/s and a periodicity of 1.3days. This radial-velocity signal is consistent with the expected variation induced by the presence a very low mass giant planetary companion to HD 41004 A, whose light dominates the spectra. The radial-velocity measurements were then complemented with a photometric campaign and with the analysis of the bisector of the CORALIE Cross-Correlation Function (CCF). While the former revealed no significant variations within the observational precision of 0.003-0.004 mag (except for an observed flare event), the bisector analysis showed that the line profiles are varying in phase with the radial-velocity. This latter result, complemented with a series of simulations, has shown that we can explain the observations by considering that HD 41004 B has a brown-dwarf companion orbiting with the observed 1.3-day period. If confirmed, this detection represents the first discovery of a brown dwarf in a very short period (1.3-day) orbit around an M dwarf. Finally, this case should be taken as a serious warning about the importance of analyzing the bisector when looking for planets using radial-velocity techniques.Comment: 16 pages, 17 eps figures, A&A in press (Figure 11 not as in original version due to size

The Observed Relationship Between Water Vapor and Ozone in the Tropical Tropopause Saturation Layer and the Influence of Meridional Transport

We examine balloonsonde observations of water vapor and ozone from three Ticosonde campaigns over San Jose, Costa Rica [10 N, 84 W] during northern summer and a fourth during northern winter. The data from the summer campaigns show that the uppermost portion of the tropical tropopause layer between 360 and 380 K, which we term the tropopause saturation layer or TSL, is characterized by water vapor mixing ratios from proximately 3 to 15 ppmv and ozone from approximately 50 ppbv to 250 ppbv. In contrast, the atmospheric water vapor tape recorder at 380 K and above displays a more restricted 4-7 ppmv range in water vapor mixing ratio. From this perspective, most of the parcels in the TSL fall into two classes - those that need only additional radiative heating to rise into the tape recorder and those requiring some combination of additional dehydration and mixing with drier air. A substantial fraction of the latter class have ozone mixing ratios greater than 150 ppbv, and with water vapor greater than 7 ppmv this air may well have been transported into the tropics from the middle latitudes in conjunction with high-amplitude equatorial waves. We examine this possibility with both trajectory analysis and transport diagnostics based on HIRDLS ozone data. We apply the same approach to study the winter season. Here a very different regime obtains as the ozone-water vapor scatter diagram of the sonde data shows the stratosphere and troposphere to be clearly demarcated with little evidence of mixing in of middle latitude air parcels

Absolute dimensions of eclipsing binaries. XXVIII. BK Pegasi and other F-type binaries: Prospects for calibration of convective core overshoot

We present a detailed study of the F-type detached eclipsing binary BK Peg, based on new photometric and spectroscopic observations. The two components, which have evolved to the upper half of the main-sequence band, are quite different with masses and radii of (1.414 +/- 0.007 Msun, 1.988 +/- 0.008 Rsun) and (1.257 +/- 0.005 Msun, 1.474 +/- 0.017 Rsun), respectively. The 5.49 day period orbit of BK Peg is slightly eccentric (e = 0.053). The measured rotational velocities are 16.6 +/- 0.2 (primary) and 13.4 +/- 0.2 (secondary) km/s. For the secondary component this corresponds to (pseudo)synchronous rotation, whereas the primary component seems to rotate at a slightly lower rate. We derive an iron abundance of [Fe/H] =-0.12 +/- 0.07 and similar abundances for Si, Ca, Sc, Ti, Cr and Ni. Yonsei-Yale and Victoria-Regina evolutionary models for the observed metal abundance reproduce BK Peg at ages of 2.75 and 2.50 Gyr, respectively, but tend to predict a lower age for the more massive primary component than for the secondary. We find the same age trend for three other upper main-sequence systems in a sample of well studied eclipsing binaries with components in the 1.15-1.70 Msun range, where convective core overshoot is gradually ramped up in the models. We also find that the Yonsei-Yale models systematically predict higher ages than the Victoria-Regina models. The sample includes BW Aqr, and as a supplement we have determined a [Fe/H] abundance of -0.07 +/- 0.11 for this late F-type binary. We propose to use BK Peg, BW Aqr, and other well-studied 1.15-1.70 Msun eclipsing binaries to fine-tune convective core overshoot, diffusion, and possibly other ingredients of modern theoretical evolutionary models.Comment: Accepted for publication in Astronomy and Astrophysic