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Query: UMLS:C0027960 (mole)
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Four of the principle apolipoproteins of murine serum have been isolated and characterized. On the basis of their physicochemical properties, they are homologous with the human and rat apoA-I, A-II, B, and C-III. The group of apolipoproteins of middle to low molecular weight, i.e., A-I, A-II and C-III, were separated from the protein moiety of high density lipoproteins (HDL) by gel filtration chromatography, followed by electrophoresis in alkaline-urea polyacrylamide gel with electrophoretic elution. Murine apoA-I, the major protein of HDL (60-80%) displayed an Mr of approximately 27,000, and was polymorphic (four prominent isoproteins with isoelectric points in the range of pH 5.5-5.7). The amino acid profiles of mouse, rat, and human apoA-I generally resembled each other, the former being distinguished by a content of one isoleucine residue per mole. Amino terminal sequence analysis revealed marked homology between the mouse, rat, dog, and human proteins; mouse and rat apoA-I differed at residues 9 and 18 with potential dissimilarities at residues 5 and 15, while the murine and canine sequences were distinct at residues 6, 9, 13, 15, and 30. Apolipoprotein A-II was a monomer, exhibiting an Mr approximately 11,000 in SDS gels; in addition, it was polymorphic (three apparent isoproteins with pI in the pH range 5.05-5.2), and resembled its human and rat counterparts in amino acid composition. ApoC-III, an acidic peptide of pI 4.74 and of Mr approximately 9,600, possessed an amino acid composition very like that of the homologous human and rat proteins. The homology of mouse apoC-III with the human protein was confirmed by NH2-terminal sequence analysis, which revealed identical amino acids in six positions (1, 2, 4, 8, 9, and 13). As shown earlier (Camus et al. 1983. J. Lipid Res. 24: 1210-1228), two forms of immunologically reacting apoB predominated in mouse VLDL and LDL. After isolation of these lipoproteins in the presence of 1 mM PMSF, the apparent sizes of the high and low Mr forms, apoBH and apoBL, were in the ranges approximately 400,000-530,000 and approximately 250,000-280,000, respectively, according to the SDS gel system. We observed that inclusion of 1 mM PMSF was essential to retard degradation of the high Mr form apoBH. The murine B proteins were isolated from apoVLDL and apoLDL by gel filtration chromatography on Sephadex G150 in anionic detergent, and displayed apparent Mr values of 460,000 (apoBH) and 250,000 (apoBL) in 3% SDS gels.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The lipid transport system in the mouse, Mus musculus: isolation and characterization of apolipoproteins B, A-I, A-II, and C-III. 643 19

When 125I-labeled thrombin was incubated with washed human platelets or with the supernatant solution of activated platelets, it formed a NaDodSO4-stable complex of apparent mass greater than 450 000 daltons. Formation of the complex was temperature dependent; with 20 nM thrombin incubated with the supernatant solution of ionophore-activated platelets, the initial rate of formation of the stable complex was 1 nM thrombin/min at 37 degrees C, 50 times the rate at 22 degrees C. Thrombin with all free amino groups methylated was still reactive. Active-site-blocked thrombin formed the complex only slowly. The complex that formed with active thrombin was not dissociated by hydroxylamine in urea. Reduction with 2-mercaptoethanol dissociated the complex, and its formation was blocked by the sulfhydryl-blocking agents iodoacetamide and 4,4'-dithiodipyridine. The complex was thus unlike those of thrombin and alpha 2-macroglobulin or antithrombin III, but it had characteristics of a disulfide-linked complex. Of the secreted proteins, albumin and glycoprotein G adhered to an activated thiol-Sepharose column, indicating that they contained free thiol groups. Purified glycoprotein G and thrombin formed a complex similar to the complex formed when thrombin was incubated with the supernatant solution of activated platelets. The purified glycoprotein bound 2.6 mol of radioactive N-ethylmaleimide/mol of protein, indicating three sulfhydryl groups per mole. After reacting with purified glycoprotein G, thrombin developed a new sulfhydryl group. It is concluded that glycoprotein G (thrombin-sensitive protein, thrombospondin) and thrombin form a dissociable complex that leads to a covalent complex by thiol-disulfide exchange of a thiol group on glycoprotein G and a disulfide on thrombin.
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PMID:Formation of a stable complex of thrombin and the secreted platelet protein glycoprotein G (thrombin-sensitive protein, thrombospondin) by thiol-disulfide exchange. 643 45

Two fractions of human prothrombin can be isolated from single donor plasma by the technique of heparin-agarose chromatography in (sodium) citrate buffer, pH 7.5, as previously reported for pooled plasma. The two fractions, designated H-II1 and H-II2, are found in a ratio of approximately 4:1. Both forms comigrate in sodium dodecyl sulfate gel electrophoresis; however, under nondenaturing electrophoretic conditions, each fraction migrates as a discrete entity with a different mobility. The larger fraction (H-II1) has a faster mobility towards the anode. Isoelectric focusing in urea of H-II1 reveals that it has two components, a minor component with a pl of 5.25 (H-II1a) and a major component with a pl of 5.40 (H-II1b). H-II2 has a pl of 5.6 H-II1 and H-II2 possess the same amino terminal residue (alanine, 0.87-0.92 mole/mole) and the same number of gamma -carboxyglutamic acid residues (9.8-10.5). Their amino acid composition is indistinguishable. However, the two fractions of prothrombin differ in their content of neutral sugar and of sialic acid residues. Removal of sialic acid with neuraminidase abolishes the electrophoretic heterogeneity. Thus, the charge heterogneity of the three variants of prothrombin found in normal human plasma appears to result exclusively from differences in the number of sialic acid residues attached to the protein moiety of the molecule.
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PMID:Heterogeneity in human prothrombin: analysis of cause. 729

Myelin basic protein (MBP) occurs in multiple forms. Three of these isoforms from human MBP (HMBP) have been highly purified. HMBP, component 1 (18.5 kDa HMBP-1), was purified by ion-exchange chromatography at pH 10.6 in 2 M urea. During this ion-exchange chromatography, a fraction (Fraction 3), which contained HMBP component 3 (monophosphorylated or deamidated 18.5 kDa) and 17.2 kDa HMBP, was collected and further purified by fast protein liquid chromatography, which separated 17.2 kDa HMBP and HMBP component 3. When the latter was subjected to limited thrombic digestion, all of HMBP component 3 not phosphorylated at theonine 98 was cleaved. This digestion mixture was separated on Sephadex, and yielded pure component 3, monophosphorylated at theonine 98 (HMBP 3pT98), for which phosphate analysis yielded approximately 1 mole P/mole protein, and NMR showed only one phosphorylation site present. Circular dichroism (CD) studies were carried out on dilute solutions of HMBP-1 (18.5 kDa), 17.2 kDa HMBP, and HMBP3pT98 (phosphorylated 18.5 kDa). The CD spectrum of HMBP-1 was similar to that reported for rabbit MBP-1 and bovine MBP-1, but the spectra of 17.2 kDa HMBP and HMBP 3pT98 were distinctly different from HMBP-1. When analyzed by best-fit computations, 17.2 kDa HMBP showed about a 9% increase of ordered structure, and a greater increase, about 12%, was estimated for HMBP3pT98, attributable to beta-structure and beta turn.
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PMID:Three isoforms of human myelin basic protein: purification and structure. 750 Mar 83

Rab5 is a Ras-related GTP-binding protein that is post-translationally prenylated with the 20-carbon isoprenoid geranylgeranyl. We have developed a method to determine the stoichiometry of prenylation of Rab5, and Rab family members in general, based on the cell-free translation of these peptides in the presence or the absence of appropriate isoprenoids. Modification of cell-free synthesized Rab5 can be monitored by following the conversion of 35S-labeled peptide to a greater mobility isoform on urea-gradient sodium dodecyl sulfate-polyacrylamide gels. The mobility-shifted isoform also incorporates radiolabel in the presence of [3H]mevalonate or [3H]geranylgeranyl pyrophosphate, confirming post-translational modification with geranylgeranyl. A quantitative assessment of the conversion of mobility-shifted Rab5, promoted by prenylation, and the amount of incorporated radiolabel from [3H]geranylgeranyl pyrophosphate was achieved by excising gel slices containing radiolabeled isoforms and measuring the covalently associated radioactivity. Using this approach, we have established that 2 moles of geranylgeranyl is attached per mole of Rab5 peptide. A 2:1 molar ratio of geranylgeranyl:peptide is observed for both Rab5wt and a truncation mutant, Rab5(1-213), containing C-terminal motifs CCXX and XXCC, respectively. When Rab proteins ending in CXC are synthesized and processed in vitro, they also incorporate geranylgeranyl at a 2:1 stoichiometry, although extended times of incubation are required for full modification. Finally, a C-terminal Rab5 truncation mutant retaining only one cysteine also becomes modified, although only a minor fraction is fully processed. This method offers a novel, quantitative approach to investigate the stoichiometry of post-translational processing of cell-free synthesized peptides without the need to purify the native molecules.
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PMID:Analysis of the stoichiometry of Rab protein prenylation. 773 57

Hydration of powdered fatty acids and their salts has been studied both in presence and absence of neutral salts, sucrose and urea using the isopiestic vapour pressure technique. Moles of water vapour adsorbed per mole or kg of soaps like sodium palmitate, sodium stearate, sodium myristate and sodium laurate have been measured in presence and absence of salts and compared with that of detergents (SDS, CTAB, DTAB and MTAB). For each case of positive excess adsorption of water vapour and negative excess adsorption of inorganic salts, urea and sucrose to different soaps, the standard free energy change (delta G degrees) per kg of substrate in bringing the bulk mole fraction from zero to unity have been calculated using an appropriate thermodynamic equation and the values so obtained have been compared critically.
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PMID:Thermodynamics of binding water and solute to powdered long-chain salts of fatty acids. 785 44

The adsorption isotherms of different proteins from aqueous solution to the surface of different solids have been compared in the presence of additives such as urea, surfactants and high concentration of various neutral salts. The adsorption isotherms of lysozyme on alumina are not affected much in the presence of 8 M urea showing the rigid structure of lysozyme whereas isotherms of hemoglobin show surface coagulation even in presence of 2 M urea. In presence of 8 M urea, adsorption isotherms of BSA on alumina show two distinct steps. The extent of protein adsorption in the presence of surfactants depends on the nature of surfactants as well as of the underlying surface. The adsorption isotherms of BSA and lysozyme in presence of 2 M concentration of different neutral salts have also been compared with each other. In the presence of denaturants such as NaI and LiCl, the proteins are adsorbed in unfolded beta-conformation whereas in the presence of protein stabilizers such as NaCl, KCl and Na2SO4, amount of protein adsorbed at saturation is zero or extremely small showing that unfolding of proteins at the interface is necessary for initial stage of protein adsorption. The standard free energy change (delta G degrees) per square meter of the surface, signifying relative affinity of adsorption at the state of monolayer saturation, have been calculated. The magnitude of standard free energy of transfer (delta G degrees B) of one mole of protein to the surface in presence of all the additives was found close to 40 kJ/mole.
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PMID:Effect of denaturants and stabilisers on protein adsorption at solid-liquid interfaces. 792 31

Transthyretin isolated by polyacrylamide gel electrophoresis from human serum and cerebrospinal fluid, dissociated into its subunits, was subjected to isoelectric focusing in polyacrylamide gels containing 8 mole/L urea. The isoelectric focusing multi-component patterns of serum and cerebrospinal fluid transthyretin differ in a characteristic way, having only one main protein zone in common. Double diffusion immunotest and immunoblotting revealed the immunological identity of serum and cerebrospinal fluid transthyretin and of the main components separated by isoelectric focusing. The different isoelectric focusing zones can be consistently explained when they are ascribed to structurally identical transthyretin subunits associated with different ligands specifically occurring in either serum or cerebrospinal fluid. Only the protein zone located at the same pI in serum and cerebrospinal fluid transthyretin patterns may be assigned to ligand-free subunits. Thus, the typical differences in isoelectric focusing patterns may point to different carrier functions of transthyretin in serum and cerebrospinal fluid.
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PMID:Differences in the isoelectric focusing patterns of serum and cerebrospinal fluid transthyretin. 812 59

Stretches of residual structure in the unfolded states of proteins could possibly constitute crucial regions that initiate protein folding. We are searching for such regions in barnase by dividing it into fragments. By this means, we can search for regions that just form within local sequences. We are also employing methods that can detect low levels of residual structure. In this study, we examine the fragment 1-22 and a large fragment (23-110) that contains all of the catalytic residues. Fragment 1-22 contains the first alpha-helix, and fragment 23-110 contains the second alpha-helix and beta-sheet structure-forming residues of native barnase. These fragments bind together rapidly and tightly upon association to form a fully native-like complex. Studies by circular dichroism and fluorescence spectroscopy indicate that each fragment is mainly disordered. However, we find by a procedure of titration with trifluoroethanol that about 3% of fragment 1-22 is helical in water at 25 degrees C. Importantly, we have detected residual catalytic activity in fragment 23-110 toward GpUp and RNA and the ability to bind the polypeptide inhibitor of barnase, barstar, suggesting that this fragment can form a native-like conformation in water. The catalytic activity does not result from a small amount of contaminating impurity of parent enzyme or other ribonuclease, since the activity requires a 1:1 mole ratio of fragment to barstar for complete inhibition, and the activity is lost in much lower concentrations of urea than are required to denature the parent enzyme. There is a very weak signal in the near-UV CD spectrum of the large fragment.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Folding of barnase in parts. 814 79

The pH titration of nine amino acids (glycine, proline, valine, serine, glutamine, tryptophan, arginine, histidine and aspartic acid) in presence of urea in the concentration range 1-8 mole dm-3 has been performed. The results support suppression of the first dissociation constant (K1) of the amino acids and acceptance of H+ ions by the amide forming uronium ion (UH+). The second dissociation constant (K2) of the amino acids is affected relatively weakly by urea. Quantitative evaluation of different species existing in solution and the degree of dissociation of the acids as well as the degree of binding of H+ ion to the amide have been made. It has been found that the polarity of the aqueous-urea medium does not straight forwardly correlate with the altered pK1 of the amino acids. Urea can also affect the pH-titration behaviour of gelatin with an increase of the intrinsic pK of the acidic groups of the protein by 0.45 unit.
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PMID:Interaction of amino acids and gelatin with urea. 814 76


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