An evaluation of the performance of an automated procedure for comparative modelling of protein tertiary structure

A 3-D model of a protein can be constructed from its amino acidsequence and the 3-D structures of one or more homologues byannealing three sets of fragments: the structurally conservedregions, structurally variable regions and the side chains.The method encoded in the computer program COMPOSER was assessedby generating 3-D models of eight proteins whose crystal structuresare already known and for which 3-D structures of homologuesare available. In the structurally conserved regions, differencesbetween modelled and X-ray structures are smaller than the differencesbetween the X-ray structures of the modelled protein and thehomologues used to build the model. When several homologuesare used, the contributions of the known structures are weighted,preferably by the square of sequence similarity; this is especiallyimportant when the similarities of the homologues to the modelledstructure differ greatly. The ‘collar’ extensionapproach, in which a similar region of different length in ahomologue is used to extend the framework, can result in a moreaccurate model. If known homologues comprise more than one relatedgroup of proteins and they are both distantly related to theunknown, then alignment of the sequence to be modelled witheach group of homologues facilitates identification of structurallyconserved regions of the unknown and leads to an improved model.Models have root mean square differences (r.m.s.d.s) with thestructures defined by X-ray analysis of between 0.73 and 1.56Å for all C atoms, for seven of the eight models. Forthe model of mucor pepsin, where the closest homologue has 33%sequence identity and 20% of the residues are in structurallyvariable regions, the r.m.s.d. for the framework region is 1.71Å and the r.m.s.d. for all C atoms is 3.47 Â.     

Behavior of biliary phospholipids in intestinal lumen during fat digestion in rat

The phospholipids present in the intestinal lumen of rats following ingestion of triglycerides are of biliary origin. They consist of lecithins accompanied by a small proportion of lysolecithins. Their behavior in comparison with the other lipid constituents of the intestinal content was studied by subjecting the latter to gel filtration on an agarose column in the presence of a solution of 6 mM sodium taurocholate in 0.1 M NaCl. Part of the phospholipids is present with the triglycerides and diglycerides in the emulsified phase excluded from the gel where pancreatic lipase and colipase also are found. The remainder is found in optically clear fractions containing fatty acids, monoglycerides, and bile salts. These fractions are eluted at 2.0 column volumes, while mixed fatty acids, monoglycerides, bile salts micelles emerge from the column at 2.4 column volumes in the same chromatographic conditions. This difference in behavior may be explained by the presence of biliary lecithins. This presence could have an important bearing upon the mucosal uptake of the lipolysis products of triglycerides.     

Graft-copolymerization of starch with acrylamide,II. Thermal behaviour of graft copolymers

Thermal behaviour of starch-graft-polyacrylamide (S-g-PAM) copolymers was evaluated. Grafting of polyacrylamide onto starch lowers the initial decomposition temperature. However, the over-all stability as assessed by the shape of thermogravimetric curve and integral procedural decomposition temperature increased with an increase in % graft-on.     

Life of stopper heads in continuous steel casting

Conclusions Chamotte heads with 5, 10 and 15% graphite differ from conventional chamotte by high thermal endurance, thermal conductivity and wear resistance. The increased rigidity of stopper heads with a graphite content of 5 to 15% used in combination with magnesite sleeves enhances the formation of longitudinal cracks.Chamotte specimens fired at 1230° C are endowed with high wear-resistance. They differ from conventional chamotte refractories by higher thermal endurance and provide for good stopper service in reladling killed steel.High-alumina SP-9-type heads made at Chasov-Yar Combine wear less in intermediate ladles and are endowed with greater thermal strength than chamotte heads.The higher quality of the chamotte heads under conditions of Stalino Metallurgical Plant in comparison to that of Krasnoye Sormovo Plant is not only due to the quality of the refractory but also to such factors as the rate and degree of preheating intermediate ladles before filling with metal, careful placement of the stoppers, and use of graphite packing around the teeming head.Despite higher wear SP-12-type chamotte heads made at Chasov-Yar Combine allowed normal teeming of rimmed steel in 50 ton ladles.To ensure a steady service of the stoppers in continuous steel casting the preheating of intermediate ladles of 1300 and the use of precooled stoppers are recommended.     

Evidence for the Microwave Effect During the Annealing of Zinc Oxide

A microwave/conventional hybrid furnace has been used to anneal virtually fully dense zinc oxide ceramics under pure conventional and a microwave/conventional hybrid heating regime with a view to obtaining evidence for the "microwave effect" during the resulting grain growth. In each case it was ensured that each sample within a series had an identical thermal history in terms of its temperature/time profile. The results showed that grain growth was enhanced during hybrid heating compared with pure conventional heating; the greatest enhancement, a factor of ∼3 increase in average grain size, was observed in the range 1100°–1150°C. The grain growth exponent decreased from 3 during conventional heating to 1.4 during hybrid heating in this temperature range, suggesting an acceleration of the diffusional processes involved. Temperature gradients within the samples were found to be too small to explain the results. This suggests that clear evidence has been found to support the existence of a genuine "microwave effect."     

Homogenous catalytic conjugation of polyunsaturated fats by chromium carbonyls

Various arene-Cr (CO)₃ complexes and Cr(CO)₆ are effective soluble catalysts for the conjugation of polyunsaturated fats. Methyl benzoate-Cr(CO)₃ is one of the most active catalysts. The following conjugation levels were obtained: methyl linoleate, 65%; methyl linolenate, 45%; the polyunsaturates in soybean and safflower oils, 73%; and in linseed oil 48%. Conjugated dienes from linoleate were predominantlycis,trans in configuration. Their double bonds were distributed between C₅ and C₁₆ of the fatty acid chain. Hydrogenation and dehydrogenation are side reactions, which seem to limit the yield of conjugated dienes from methyl linoleate. A conjugation mechanism is proposed that involves allyl-HCr(CO)₃ complexes as intermediates undergoing 1,3- and 1,5-hydrogen shifts. Presented at the AOCS Meeting, San Francisco, April 1969. No, Utiliz. Res. Dev. Div., ARS, USDA.     

Viscoelastic characteristics of mixed compositions based on polyethylene and polypropylene

VNIISV, Tver'. Institute of Chemical Physics, Moscow. Translated from Khimicheskie Volokna, No. 3, pp. 42–43, May–June, 1992.     

Corundum hydraulically hardening rammed compounds with a reduced grain size

Conclusions The production and use of rammed hydraulically hardening corundum compounds with different maximum grain sizes (from 1 to 7 mm) permits intermediate repairs of the linings of ladles of a steel ladle treatment unit, increasing their life.It is possible to determine the quantity of binder for obtaining the maximum strength by calculation by use of the coefficient of optimization, which is the portion of binder required per unit of specific surface of the mixture of filler grains. For the corundum hydraulically hardening compounds the optimum value of this coefficient is 0.8–1.2.Translated from Ogneupory, No. 2, pp. 40–43, February, 1987.     

Dietary effect of a symmetrical triacylglycerol, 1,3-biseicosapentaenoyl-2-γ-linolenoyl glycerol, on fatty acid composition of guinea pigs

The dietary effect of 1,3-biseicosapentaenoyl-2-γ-linolenoyl glycerol (STG) on the fatty acid composition of guinea pigs was examined and compared with that of an eicosapentaenoic acid ethyl ester (EPA-F) and of a soybean oil (SBO) diet. In terms of content of plasma lipid, EPA-E had a greater hypolipidemic effect than STG. On the other hand, in terms of EPA incorporation, contents of EPA in liver lipid were almost the same in the STG and EPA-E groups. Considering that the amount of EPA administered in the EPA-E group was almost 1.5 times that of the STG group, FPA may be absorbed more effectively as the glycerol ester than as the ethyl ester in guinea pigs. In all the tissue lipids, the STG group had a higher unsaturation index (UI) than the EPA-E group even though there is a lower UI in the STG diet than the EPA-E diet. These results suggest that greater amounts of desaturase products as a whole were synthesized in the STG group than in the other two groups. The dihomo-γ-linolenic acid/arachidonic acid (DGLA/AA) ratio in plasma total lipids in the STG group was 3.5 times that of SBO group, and the DGLA/AA ratio in the EPA-E group was half that of the SBO group. In liver lipid, the ratios of DGLA/AA and EPA/AA in the STG group were 0.687 and 0.488 (phosphatidylcholine fraction) and 0.237 and 0.752 (phosphatidylethanolamine fraction), respectively. The ratio of DGLA/AA as well as the high EPA/AA ratio obtained in the present study with the STG diet may lead to physiological alterations, including enhanced synthesis of 1-and 3-series eicosanoids.