Hydrophobic sequence minimization of the α-lactalbumin molten globule

The molten globule, a widespread protein-folding intermediate, can attain a native-like backbone topology, even in the apparent absence of rigid side-chain packing. Nonetheless, mutagenesis studies suggest that molten globules are stabilized by some degree of side-chain packing among specific hydrophobic residues. Here we investigate the importance of hydrophobic side-chain diversity in determining the overall fold of the α-lactalbumin molten globule. We have replaced all of the hydrophobic amino acids in the sequence of the helical domain with a representative amino acid, leucine. Remarkably, the minimized molecule forms a molten globule that retains many structural features characteristic of a native α-lactalbumin fold. Thus, nonspecific hydrophobic interactions may be sufficient to determine the global fold of a protein.

Thermal unfolding of human high-density apolipoprotein A-1: implications for a lipid-free molten globular state.

Apolipoprotein A-1 (apoA-1) in complex with high-density lipoprotein is critically involved in the transport and metabolism of cholesterol and in the pathogenesis of atherosclerosis. We reexamined the thermal unfolding of lipid-free apoA-1 in low-salt solution at pH approximately 7, by using differential scanning calorimetry and circular dichroism. At protein concentrations <5 mg/ml, thermal unfolding of apoA-1 is resolved as an extended peak (25 degrees C-90 degrees C) that can be largely accounted for by a single reversible non-two-state transition with midpoint Tm 57 +/- 1 degree C, calorimetric enthalpy deltaH(Tm)= 200 +/- 20 kcal/mol (1 kcal = 4.18 kJ), van't Hoff enthalpy deltaHv(Tm) approximately 32.5 kcal/mol, and cooperativity deltaHv(Tm)/deltaH(Tm) approximately 0.16. The enthalpy deltaH(Tm) can be accounted for by melting of the alpha-helical structure that is inferred by CD to constitute approximately 60% of apoA-1 amino acids. Farand near-UV CD spectra reveal noncoincident melting of the secondary and tertiary structural elements and indicate a well-defined secondary structure but a largely melted tertiary structure for apoA-1 at approximately 37 degrees C and pH 7. This suggests a molten globular-like state for lipid-free apoA-1 under near-physiological conditions. Our results suggest that in vivo lipid binding by apoA-1 may be mediated via the molten globular apolipoprotein state in plasma.

Structure and stability of a second molten globule intermediate in the apomyoglobin folding pathway.

Apomyoglobin folding proceeds through a molten globule intermediate (low-salt form; I1) that has been characterized by equilibrium (pH 4) and kinetic (pH 6) folding experiments. Of the eight alpha-helices in myoglobin, three (A, G, and H) are structured in I1, while the rest appear to be unfolded. Here we report on the structure and stability of a second intermediate, the trichloroacetate form of the molten globule intermediate (I2), which is induced either from the acid-unfolded protein or from I1 by > or = 5 mM sodium trichloroacetate. Circular dichroism measurements monitoring urea- and acid-induced unfolding indicate that I2 is more highly structured and more stable than I1. Although I2 exhibits properties closer to those of the native protein, one-dimensional NMR spectra show that it maintains the lack of fixed side-chain structure that is the hallmark of a molten globule. Amide proton exchange and 1H-15N two-dimensional NMR experiments are used to identify the source of the extra helicity observed in I2. The results reveal that the existing A, G, and H helices present in I1 have become more stable in I2 and that a fourth helix--the B helix--has been incorporated into the molten globule. Available evidence is consistent with I2 being an on-pathway intermediate. The data support the view that apomyoglobin folds in a sequential fashion through a single pathway populated by intermediates of increasing structure and stability.

Surface growth for molten silicon infiltration into carbon millimeter-sized channels: Lattice–Boltzmann simulations, experiments and models

The process of liquid silicon infiltration is investigated for channels with radii from 0.25 to 0.75 [mm] drilled in compact carbon preforms. The advantage of this setup is that the study of the phenomenon results to be simplified. For comparison purposes, attempts are made in order to work out a framework for evaluating the accuracy of simulations. The approach relies on dimensionless numbers involving the properties of the surface reaction. It turns out that complex hydrodynamic behavior derived from second Newton law can be made consistent with Lattice-Boltzmann simulations. The experiments give clear evidence that the growth of silicon carbide proceeds in two different stages and basic mechanisms are highlighted. Lattice-Boltzmann simulations prove to be an effective tool for the description of the growing phase. Namely, essential experimental constraints can be implemented. As a result, the existing models are useful to gain more insight on the process of reactive infiltration into porous media in the first stage of penetration, i.e. up to pore closure because of surface growth. A way allowing to implement the resistance from chemical reaction in Darcy law is also proposed.

Molten salts : selected references /

"Included are 205 references to unclassified reports received by the Office of Technical Information Extension since mid-1958"--Page [1].

Molten salts : selected references /

Includes indexes.

Heat Transfer to molten lead-bismuth eutectic in turbulent pipe flow /

"Contract No. AT-(40-1)-1061 Part 2."

The application of X-ray examination and inspection to: castings ... welding ... food products ... X-ray diffraction.

Cover-title: Industrial applications of the X-ray.

ASTM specifications for steel piping materials; pipe, tubes, castings, forgings [and] bolting.

Mode of access: Internet.

Development of low alloy steel compositions suitable for high strength steel castings

Mode of access: Internet.

Casting Kaiser aluminum: pig and ingot product data, casting practices, and characteristics of molten aluminum.

Mode of access: Internet.

Recommended practice for the welding of steel castings.

Bibliography: p.38-39.

The feasibility of reclaiming investment shell material from investment castings /

"Printed January 1992."