Solidus surface of the Ti-Ru-Ir system

Conclusions The interaction of the components in the Ti-Ru-Ir system at the subsolidus temperatures was examined. Intermediate phases differing from those existing in the limiting binary systems were not detected. The equiatomic phases TiRu and TiIr which are isostructural at high temperatures form a continuous series of the solid solutions. The solubility of ruthenium in TiIr₃ reaches 27%, and in Ti₃Ir ruthenium does not dissolve. The solidus surface of the system contains three isothermal planes whose temperatures (2220, 1920, 1465C) decrease with increasing ruthenium and titanium content of the alloys. The lowest solidus temperature of the Ti-Ru-Ir system is the melting point of the -Ti + Ti₃Ir binary eutectic of the Ti-Ir system (1460C).Translated from Poroshkovaya Metallurgiya, No. 10(298), pp. 69–73, October, 1987.     

Protein engineering the surface of enzymes

The protein surface is the interface through which a protein senses the external world. Its composition of charged, polar and hydrophobic residues is crucial for the stability and activity of the protein. The charge state of seven of the twenty naturally occurring amino acids is pH dependent. A total of 95% of all titratable residues are located on the surface of soluble proteins. In evolutionary related families of proteins such residues are particularly prone to substitutions, insertions and deletions. We present here an analysis of the residue composition of 4038 proteins, selected from 125 protein families with < 25% identity between core members of each family. Whereas only 16.8% of the residues were truly buried, 40.7% were > 30% exposed on the surface and the remainder were < 30% exposed. The individual residue types show distinct differences. The data presented provides an important new approach to protein engineering of protein surfaces. Guidelines for the optimization of solvent exposure for a given residue are given. The cutinase family of enzymes has been investigated. The stability of native cutinase has been studied as a function of pH, and has been compared with the cutinase activity towards tributyrin. Whereas the onset of enzymatic activity is linked with the deprotonation of the active site HIS188, destabilization of the 3D structure as determined by differential scanning calorimetry is coupled with the loss of activity at very basic pH values. A modeling investigation of the pH dependence of the electrostatic potentials reveals that the activity range is accompanied by the development of a highly significant negative potential in the active site cleft. The 3D structures of three mutants of the Fusarium solani pisi cutinase have been solved to high resolution using X-ray diffraction analysis. Preliminary X-ray data are presented.     

Stress at the pleural surface

The transmission of forces between the visceral and parietal pleural is modelled as being mediated by two distinct pathways: (a) a contact pressure (Pcon) acting on an area of contact (Acon) and (2) a pleural liquid pressure (Pliq) acting on the area of liquid anfractuosities (Aliq). Summation of the forces yields a new equation relating pleural surface pressure (Ppl) to Pcon, Acon, Pliq, and Aliq. A complete solution of the equation is restricted by present limitations on measurement technology. However, assuming that the volume of pleural liquid is constant during tidal breathing, analysis of the model explains the findings that tidal swings in Pliq (deltaPliq) are sometimes greater than tidal swings in Ppl (deltaPpl). It also predicts that the influence of a change of lung elastic recoil on Pliq may be different in magnitude than its effect on Ppl. Therefore deltaPliq is not necessarily equivalent to deltaPpl.     

Roughness of the globular protein surface]

The area and volume of the approximating ellipsoids taken from low resolution X-ray data have been calculated for 65 globular proteins. It has been shown that the dependence of these values on the protein molecular mass (M) coincides with those for even isometric bodies. This indicates that the asymmetry of globular proteins does not grow with the increase of their sizes. At the same time the 0.73 slope of the log-log dependence of the accessible surface area (A(s)) on the protein molecular mass differing from the value of 0.67 for even isometric bodies was observed (Miller S. et al., J. Mol. Biol. 1987. V.196. P.641). This can be explained by peculiarities of the protein surface. The method of molecule shape recovery by spherical harmonics has shown that the domain organization of protein molecule cannot explain the observed difference. Therefore the more detailed analysis of protein surface structure would be necessary.