Amphiphilic cationic peptides mediate cell adhesion to plastic surfaces

Four amphiphilic peptides, each with net charges of +2 or more at neutrality and molecular weights under 4 kilodaltons, were found to mediate the adhesion of normal rat kidney fibroblasts to polystyrene surfaces. Two of these peptides, a model for calcitonin (peptide 1, MCT) and melittin (peptide 2, MEL), form amphiphilic alpha-helical structures at aqueous/nonpolar interfaces. The other two, a luteinizing hormone-releasing hormone model (peptide 3, LHM) and a platelet factor model (peptide 4, MPF) form beta-strand structures in amphiphilic environments. Although it contains only 10 residues, LHM mediated adhesion to surfaces coated with solutions containing as little as 10 pmoles/ml of peptide. All four of these peptides were capable of forming monolayers at air-buffer interfaces with collapse pressures greater than 20 dynes/cm. None of these four peptides contains the tetrapeptide sequence Arg-Gly-Asp-Ser, which has been associated with fibronectin-mediated cell adhesion. Ten polypeptides that also lacked the sequence Arg-Gly-Asp-Ser but were nonamphiphilic and/or had net charges less than +2 at neutrality were all incapable of mediating cell adhesion (Pierschbacher and Ruoslahti, 1984). The morphologies of NRK cells spread on polystyrene coated with peptide LHM resemble the morphologies on fibronectin-coated surfaces, whereas cells spread on surfaces coated with MCT or MEL exhibit strikingly different morphologies. The adhesiveness of MCT, MEL, LHM, and MPF implies that many amphiphilic cationic peptides could prove useful as well defined adhesive substrata for cell culture and for studies of the mechanism of cell adhesion.     

The catalytic mechanism of bovine intestinal 5'-nucleotide phosphodiesterase. pH and inhibition studies

Extensive kinetic studies of bovine intestinal 5'-nucleotide phosphodiesterase as a function of pH have confirmed and amplified the catalytic mechanism previously proposed on the basis of isolation of a covalent phosphorylated intermediate (Landt, M., and Butler, L.G. (1978) Biochemistry 17, 4130-4135). An enzyme-ionizing group with apparent pKa = 6.85 controls the rate-determining step. Electrostatic interactions between anionic substrate and two or more ionic groups on the enzyme have a major role in substrate binding. Binding of strongly inhibitory 5'-AMP is controlled by an ionizing group, probably on the enzyme, with pKa less than or equal to 5.9. At pH 6.0, imidazole is a classic uncompetitive inhibitor, in agreement with independent evidence that it stabilizes the covalent intermediate form of the enzyme. KI values for phosphonate analogs, which are competitive inhibitors, indicate that phosphodiesterase binds its products and product analogs more strongly than it binds substrate analogs. Some of the results presented here can be interpreted as indicating that 5'-nucleotide phosphodiesterase is the evolutionary precursor of alkaline phosphatase, with which it has many structural and catalytic properties in common, and which is found in relatively large amounts in the same tissue.     

A new approach for estimating the crosslink density of covalently crosslinked ionic polysaccharide gels

For an ideal polysaccharide gel with a known total polymer chain contour length, crosslinks all of the same functionality and elastic chains all with the same contour length and stiffness, the gel crosslink density can readily be determined from measurements of the maximum volume of the swollen gel (Moe et al., (1991) Food Hydrocolloids, 5, (1/2), 119–123. In the case of randomly crosslinked polysaccharide gels, where the chain contour length between two adjacent crosslinks may vary greatly, it is often much more difficult to determine the crosslink density. This paper reports on an attempt to extend the use of maximum gel volume measurements to estimate crosslink density for the latter type of gel. This is done by calculating the maximum swelling volume for polymer networks with four-functional crosslinks, known elastic chain mean contour length and standard deviation. The numerical analysis involves the calculation of the equilibrium force at each crosslink as the network expands. This allows a detailed study of how the distribution of individual polymer chain contour lengths affects the maximum swelling volume. The computer simulation results are compared with the results from experimental measurements of the maximum volume of swollen covalently crosslinked sodium alginate gels.     

Molecular cut-off values of dialysis membranes for alginate and kappa-carrageenan oligosaccharides

The effective molecular weight cut-off values of dialysis membranes for carrageenan and alginate oligosaccharides were evaluated by gel permeation chromatography and nuclear magnetic resonance spectroscopy. For the different membranes tested, i.e. Medicell, Spectra Por 1000D and 3500D, the porous sizes are analogous to tri- and tetrasaccharides. A simple dialysis can be used to recover the majority of the oligosaccharides produced by a carrageenase or an alginate lyase digestion.     

Biotin carboxylases in mitochondria and the cytosol from skeletal and cardiac muscle as detected by avidin binding

Biotin carboxylases in mammalian cells are regulatory enzymes in lipogenesis and gluconeogenesis. In this study, endogenous biotin in skeletal and cardiac muscle was detected using avidin conjugated with alkaline phosphatase and applied in high concentrations to muscle sections. The avidin binding was subsequently visualized by histochemical demonstration of the alkaline phosphatase activity. All cardiac muscle cells showed high affinity for avidin with only the nuclei and the intercalated discs remaining unstained. In skeletal muscle a diffuse reaction could be detected in the sarcoplasm of the muscle fibres. A granular reaction was noted in the same fibres that showed activity for succinic dehydrogenase. The specificity of the coloured reaction product in the muscle sections was investigated and is suggested to be caused by avidin binding to biotin moieties in mitochondria and the cytosol. Mitochondrial and cytosolic preparations of skeletal muscle were electrophoresed in sodium dodecyl sulphate gels. After blotting and incubation with conjugated avidin, two bands with molecular weights of 75 kDa and 130 kDa respectively were evident in the mitochondrial preparation. It is suggested that the 75-kDa band represents comigration of the biotin-containing subunits of propionyl-CoA carboxylase and methylcrotonyl-CoA carboxylase. The 130-kDa band may represent the biotin-containing pyruvate carboxylase. In the cytosolic preparation a 270-kDa band was stained in blots that had been incubated with conjugated avidin; this band is suggested to represent acetyl-CoA carboxylase. A 190-kDa cytosolic band might be a cleavage product of acetyl-CoA carboxylase. We propose that using alkaline phosphatase-conjugated avidin it is possible to detect the mitochondrial and cytosolic biotin-dependent carboxylases in striated muscle.     

Circular dichroism of the parallel β helical proteins pectate lyase C and E

The pectate lyases, PelC and PelE, have an unusual folding motif, known as a parallel β-helix, in which the polypeptide chain is coiled into a larger helix composed of three parallel β-sheets connected by loops having variable lengths and conformations. Since the regular secondary structure consists almost entirely of parallel β-sheets these proteins provide a unique opportunity to study the effect of parallel β-helical structure on circular dichroism (CD). We report here the CD spectra of PelC and PelE in the presence and absence of Ca²⁺, derive the parallel β-helical components of the spectra, and compare these results with previous CD studies of parallel β-sheet structure. The shape and intensity of the parallel β-sheet spectrum is distinctive and may be useful in identifying other proteins that contain the parallel β-helical folding motif. © 1995 Wiley-Liss, Inc.     

The Late Quaternary history of Rhamnus frangula in Norway

Finds of pollen and macrofossils of Rhamnus frangula L. from Eem and Holocene are discussed and compared with the present pollen production and dispersal of the species, and its present distribution. It is presumed that there was little difference between the potential distribution area of R. frangula and its actual geographical range because of its rapid spread during Preboreal and Boreal in South Norway. A small, temporary expansion of R. frangula occurred around 5 500 BP in a mountain valley in W Norway. A simultaneous local expansion of the species has been registered in Vestvågøy, Nordland county, N Norway. In these two areas, which are outside its present distribution, the maximum of R. frangula is dated to between 5 000 and 4 800 BP. The maxima of R. frangula in profiles from other Norwegian areas are discussed. Factors such as changes in climatic condition, in–filling stages of local successions in the sedimentation basins, or human activity may explain the differences found.     

Lectin binding in skeletal muscle. Evaluation of alkaline phosphatase conjugated avidin staining procedures

Summary Cryostat sections from rat gracilis muscles were incubated with different biotinylated lectins: Con A (Concanavilin A), WGA (Wheat germ agglutinin), SBA (soybean agglutinin), GS I and GS II (Griffonia simplicifolia agglutinin), LCA (Lens culinaris agglutinin), PNA (peanut agglutinin) and PSA (Pisum sativum agglutinin). The sections were subsequently treated with alkaline phosphatase conjugated avidin. The lectin binding sites were visualized after incubation in substrate media containing: (1) 5-bromo-4-chloro indoxyl phosphate and Nitro Blue tetrazolium or copper sulphate; (2) naphthol AS-MX phosphate or naphthol AS-BI phosphate and various types of diazonium salts; (3) -naphthylphosphate and Fast Blue BB; (4) -glycerophosphate according to the method of Gomori. The results obtained with the alkaline phosphatase methods were compared with those seen with a streptavidin-horseradish peroxidase procedure. Several chromogen protocols for visualizing alkaline phosphatase activity showed differences in the ability to detect lectin binding sites. A sarcoplasmic reaction was evident for Con A, GS II, WGA, LCA, and PSA after incubation in the indoxyl phosphate medium. Sarcoplasmic reaction for GS II was also noticed after incubation with naphthol AS-MX Fast Blue BB and -glycerophosphate. The latter substrate also gave rise to a sarcoplasmic Con A reaction. With the indoxylphosphate tetrazolium salt method some muscle fibres showed a very strong intracellular reaction after incubation with Con A and GS II while the staining intensity was weak in other fibres. The same muscle fibres were stained with PAS. No sarcoplasmic reactions were observed with either naphthol phosphate media or with the diaminobenzidine peroxidase methods. Further, the staining of the muscle fibre periphery, connective tissue, and capillaries was intensified using the indoxyl method. The indoxylphosphate-tetrazolium salt method seems to be suitable for future investigations of lectin binding sites in muscle sections.     

Isoleucyl transfer ribonucleic acid synthetase. Competitive inhibition with respect to transfer ribonucleic acid by blue dextran.

The inhibitory effects of blue dextran and a small dye molecule derived from it (F3GA-OH) on the steady-state reaction catalyzed by Escherichia coli isoleucy-tRNA synthetase have been studied. Blue dextran gave uncompetitive inhibition with respect to Mg.ATP, mixed inhibition with respect to L-isoleucine, and competitive inhibition with respect to tRNA. The small dye molecule (F3GA-OH) was also competitive with respect to tRNA. These inhibition patterns were not consistent with the bi-uni-uni-bi Ping Pong mechanism generally accepted for aminoacyl-tRNA synthetases. They were consistent with a mechanism in which a second L-isoleucine is bound after isoleucyl-AMP synthesis and before transfer of the isoleucyl moiety to tRNA. Enzyme-bound L-isoleucine lowered the affinity of the enzyme for blue dextran approximately fivefold, a value comparable to the ninefold lowering of the enzyme's affinity for tRNA upon binding L-isoleucine. The affinity of the synthetase for F3GA-OH (K1 = 1.0 X 10(-7) M) is approximately fivefold higher than its affinity for blue dextran (K1 = 5.3 X 10(-7) M). These results indicate that blue dextran and its derivatives may be useful for kinetic and physical studies of polynucleotide binding sites on proteins as well as NAD and ATP sites.