Core packing

Frozen fish fingers and similar products are made from a mixture of different fish that arrive at the processing plant as frozen blocks of the average size 62.7 x 254 x 482 mm (thick x width x length). The frozen blocks are minced and the still frozen minced fish blocks are mixed and pressed into the desired shape, covered with batter and bread crumbs, baked on the outside (still with a frozen core), packed and stored in a deep freezer. 

WA Lim, A Hodel, RT Sauer, FM Richards. The crystal structure of a mutant protein with altered but improved hydrophobic core packing. Proc Natl Acad Sci USA 91 423-427, 1994. PB Harbury, B Tidor, PS Kim. Repacking proteins cores with backbone freedom Structure prediction for coiled coils. Pi oc Natl Acad Sci USA 92 8408-8412, 1995. 

Flow Tests. One foot long sand packs using Wilmington oil field unconsolidated sand were prepared for each of the flow tests. Porosity and permeability of all the sand packs were within 30-35% and 100-300 md, respectively. All core packs were evacuated to about 1 mm of mercury (Hg) before saturating them under gravity to assure complete water saturation. Table III gives the core and fluid properties for the flow tests. The properties of the cores were chosen so that they are close to the field conditions reported by Krebs(15). 

In the next run, a core pack was saturated with 8.6 cp (at 50° C) Ranger-zone crude oil and water flooded to residual oil saturation. Polymer flood was then initiated and about 1.2% of the original oil in place (OOIP) was recovered. The results are shown in Figure 4. The pressure profiles show behavior essentially similar to the previous run except that the pressure drop across the core increased to 100 psi within 4 PV of injection of polymer. The steady state values of pH and viscosity were 7.0 and 0.7 cp. respectively. The oil ganglia retained in larger pores resisting displacement probably reduced the amount of polymer adsorbed and reduced the number of pores that the polymer molecules needed to seal off in order to block the core. This could explain the more rapid plugging of the core. Effluent pH and viscosities remained much lower than influent values. 

Fig. 6. Model of a typical coiled coil dimer with focus on hydrophobic core packing and interhelical salt bridges. (See Colour Plate Section at the end of this book.)...

Fig. 9. Coiled-coil spirals. For the phage coat proteins and flagellin, subunits are shown enlarged next to the structures, as well as the cross sections of the coiled-coil sheets they form. The positions of the subunits in the structures are indicated in white. The core packing layers are also shown for the phage coat proteins in order to illustrate the use of knobs-into-holes and ridges-into-grooves layers.

Interestingly, when the buried Asn was replaced by Leu, structural specificity was lost and the peptides formed a heterotetramer without fixed helix-helix orientations (Lumb and Kim, 1995). In a further report on this system, Sia and Kim (2001) showed that the two copies of Acid-pl in the heterotetramer could be replaced by a peptide, D-Acid, in which all of the residues were made from D-amino acids. This clever redesign was guided by helical-net diagrams that considered core packing in the D/L structure. These revealed a d rather than a a and d d layers in the core, which were accommodated in the new design by a half-heptad shift of a redesigned L-Base sequence. 

Raine, A. R., Scrutton, N. S., and Mathews, F. S., 1994, On the evolution of alternate core packing in eightfold beta/alpha- barrels, Protein Sci 3 1889-1892. 

Hurley JH, Baase WA, Matthews BW. Design and structural analysis of alternative hydrophobic core packing arrangements in bacteriophage T4 lysozyme. J. Mol. Biol. 1992 224 1143-1159. 44. 

Resell, C. M. and Vaidya, A. M., Twin-core packed-bed reactors for organic-phase enzymatic esterification with water activity control, App. Microbiol. Biotechnol., 44, 283-286, 1995. 

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