Analysis of disulphide linkages in bovine kappa-casein oligomers using two-dimensional electrophoresis

Disulphide bonds play an important role in protein structure and function. Bovine kappa-casein (kappa-csn), an important glycoprotein in milk, contains two cysteines that can form disulphide bonds. On 2-D gels run under nonreducing conditions the kappa-csn in milk presented a complex pattern of monomers and disulphide-linked oligomers. Trains of spots corresponding to monomers to hexamers were observed as a result of the participation of different glycoforms and phosphoforms in oligomer formation. The dimers and trimers ran as doublets on the gel and analysis of the disulphide-linked peptides released from them after in-gel tryptic digestion showed they were the result of different disulphide linkages. The linkages were confirmed by MSMS. When milks with electrophoretically distinct genetic variants of kappa-csn were mixed and run on 2-D gels, they retained their distinct patterns indicating that disulphide exchange reactions or disulphide 'scrambling' was not occurring during 2-D analysis. The patterns observed represent the native distribution of kappa-csn in milk at harvest. The role and significance of the disulphide bonding of kappa-csn are discussed.     

Extending the disjoint‐representatives theorems of Hall,Halmos, and Vaughan to list‐multicolorings of graphs

Philip Hall's famous theorem on systems of distinct representatives and its not‐so‐famous improvement by Halmos and Vaughan (1950) can be regarded as statements about the existence of proper list‐colorings or list‐multicolorings of complete graphs. The necessary and sufficient condition for a proper “coloring” in these theorems has a rather natural generalization to a condition we call Hall's condition on a simple graph G, a vertex list assignment to G, and an assignment of nonnegative integers to the vertices of G. Hall's condition turns out to be necessary for the existence of a proper multicoloring of G under these assignments. The Hall‐Halmos‐Vaughan theorem may be stated: when G is a clique, Hall's condition is sufficient for the existence of a proper multicoloring. In this article, we undertake the study of the class HHV of simple graphs G for which Hall's condition is sufficient for the existence of a proper multicoloring. It is shown that HHV is contained in the class ℋ︁₀ of graphs in which every block is a clique and each cut‐vertex lies in exactly two blocks. On the other hand, besides cliques, the only connected graphs we know to be in HHV are (i) any two cliques joined at a cut‐vertex, (ii) paths, and (iii) the two connected graphs of order 5 in ℋ︁₀, which are neither cliques, paths, nor two cliques stuck together. In case (ii), we address the constructive aspect, the problem of deciding if there is a proper coloring and, if there is, of finding one. © 2000 John Wiley & Sons, Inc. J Graph Theory 33: 199–219, 2000     

Infrared absorption of some high-purity chalcogenide glasses

New compouning techniques were devised to prepare high-purity Ge₂₈Sb₁₂Se₆₀ (TI 1173)and Ge₃₃As₁₂Se₅₅ TI 20). The methods were based on the combination of the reactant purification and compounding steps. The goal of the program was to establish the absorption limit for the glasses and to lower the absorption at 10.6 μm. At the present purity level, the GeSbSe glass is found to have an absorption level of about 0.01 cm^?1 at 10.6 μm while the absorption level for the GeAsSe glass is 0.05 cm^?1. Underlying causes for the limits are discussed along with the possibilities for improvement.     

Coloring graphs which have equibipartite complements

If G is a graph of order $2n \geq 4$ with an equibipartite complement, then G is Class 1 (i.e., the chromatic index of G is Δ (G)) if and only if G is not the union of two disjoint K_n's with n odd. Similarly if G is a graph of order 2n ≥ 6 whose complement G is equibipartite with bipartition (A, D), and if both G and B, the induced bipartite subgraph of G with bipartition (A, D), have a 1-factor, then G is Type 1 (i.e., the total chromatic number of G is Δ (G) + 1). © 1997 John Wiley & Sons, Inc. J Graph Theory 26: 183–194, 1997     

r‐Regular,r‐connected decompositions of complete graphs

If r|(n‐1) and rn is even, then K_n can be expressed as the union of edge‐disjoint isomorphic r‐regular r‐connected factors. © 2000 John Wiley & Sons, Inc. J Combin Designs 8: 15–21, 2000     

Using indirect covariance spectra to identify artifact responses in unsymmetrical indirect covariance calculated spectra

Several groups of authors have reported studies in the areas of indirect and unsymmetrical indirect covariance NMR processing methods. Efforts have recently focused on the use of unsymmetrical indirect covariance processing methods to combine various discrete two-dimensional NMR spectra to afford the equivalent of the much less sensitive hyphenated 2D NMR experiments, for example indirect covariance (icv)-heteronuclear single quantum coherence (HSQC)-COSY and icv-HSQC-nuclear Overhauser effect spectroscopy (NOESY). Alternatively, unsymmetrical indirect covariance processing methods can be used to combine multiple heteronuclear 2D spectra to afford icv-13C-15N HSQC-HMBC correlation spectra. We now report the use of responses contained in indirect covariance processed HSQC spectra as a means for the identification of artifacts in both indirect covariance and unsymmetrical indirect covariance processed 2D NMR spectra.     

Multistep correlations via covariance processing of COSY/GCOSY spectra: opportunities and artifacts

Long-range homonuclear coupling pathways can be observed in COSY or GCOSY spectra by the acquisition of spectra with larger numbers of increments of the evolution period, t(1), than would normally be used. Alternatively, covariance processing of COSY-type spectra acquired with modest numbers of t(1) increments, allows the observation of multistage correlations. In this work results obtained from covariance-processed GCOSY spectra are fully analyzed and compared to normally processed COSY and 80 ms TOCSY spectra. Multistage or 'RCOSY-type' correlations are observed when remote protons both exhibit correlations to the same coupling partner e.g. A --> B and B --> C gives rise to an A --> C correlation. In the strict sense, RCOSY-type responses are artifacts albeit providing useful information. Nonbeneficial artifact correlations are observed when protons couple to other protons that overlap or partially overlap. The origin of artifact responses is also analyzed.     

The rapid characterisation of poly(ethylene glycol) oligomers using desorption electrospray ionisation tandem mass spectrometry combined with novel product ion peak assignment software

A rapid method for the characterisation of polyglycol esters and ethers is described which uses accurate mass desorption electrospray ionisation (DESI) quadrupole time-of-flight mass spectrometry (Q-ToFMS). The results are combined with newly developed software which aids the interpretation of product ions produced using collision-induced dissociation (CID) of selected precursor ions. The poly(ethylene glycol) (PEG) samples analysed were PEG dibenzoate, PEG monooleate, PEG butyl ether, PEG bis(2-ethyl hexanoate) and PEG diacrylate. Lithium metal was used for cationisation of the PEG oligomers since it yielded the most useful structural information compared with other group I metals. The full scan mass spectra and product ion mass spectra were all obtained in <5 s. Interpretation of the MS/MS product ion spectra, using the product ion interpretation software which incorporates previously developed fragmentation rules, was carried out in <1 s.     

18,18'-Dihexyl[9,9']biphenanthro[9,10-b]triphenylene: construction and consequences of a profoundly hindered aryl-aryl single bond

The title compound, 1-Hex, was synthesized by the Zr-mediated biphenylation of 4,4'-dihexyloctabromobiphenyl using (Li(THF)4)2 x Zr(biphe)3, where biphe is the 2,2'-biphenyldiyl ligand, in 5% isolated yield. Two independent X-ray diffraction analyses revealed that arene 1-Hex possesses a highly strained and hindered aryl-aryl single bond. This bond causes the phenanthro[9,10-b]triphenylene (PTP) moieties to twist (anthracene subunit dihedral, 69 degrees); the interlocked, helical, homochiral PTP moieties give rise to effective D2 symmetry. The calculated adiabatic homolytic bond dissociation energy of this strained bond is only 67 kcal/mol, but nonetheless the bond exhibits a surprisingly normal length (1.49 A); the reason is elongation only slowly releases strain. Variable temperature NMR revealed two dynamic processes: hexyl rotation (12.0 +/- 0.4 kcal/mol) and inversion of chirality (15.2 +/- 0.6 kcal/mol). DFT calculations provide rate-determining transitions states, whose energies agree with measured values, and provide insight to the mechanism of these processes. Rotation about the central bond is not involved in either observed process. Calculations demonstrate that rotation does not involve a simple torsion of the equilibrium structure, but rather a complex movement with a barrier of 49 kcal/mol from a slipped-parallel, C(2h) intermediate.