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At least 523 records · Page 29Linked to original sources
PubMed1983

Stability and melting kinetics of structural domains in the myosin rod.

The thermal stability and melting kinetics of the alpha-helical conformation within several regions of the rabbit myosin rod have been investigated. Cyanogen bromide cleavage of long myosin subfragment-2 produced one coiled-coil alpha-helical fragment corresponding to short subfragment-2 with molecular weight 90,000 (Mr = 45,000) and two fragments from the hinge region with molecular weights of 32,000 to 34,000 (Mr = 16,000 to 17,000) and 24,000 to 26,000 (Mr = 12,000 to 13,000). Optical rotation melting experiments and temperature-jump kinetic studies of long subfragment-2 and its cyanogen bromide fragments show that the hinge and the short subfragment-2 domains melt as quasi-independent co-operative units. The alpha-helical structure within the hinge has an appreciably lower thermal stability than the flanking short subfragment-2 and light meromyosin regions of the myosin rod. Two relaxation processes for helix-melting, one in the submillisecond range (tau f) and the other in the millisecond range (tau s), are observed in the light meromyosin and short subfragment-2 regions of the rod, but melting in the hinge domain is dominated by the fast (tau f) process. Results suggest that the hinge domain of the subfragment-2 link may be the locus of force generation in a cycling cross-bridge.

Amino Acids↗
PubMed1991

Cyanohydrin glycosides with unusual sugar residues: revised structure of passitrifasciatin.

The cyclopentanoid cyanohydrin glycoside passitrifasciatin was reisolated, and shown to be (1S,4R)-1-(beta-D-gluopyranosyloxy)-4-(6-deoxy-beta-D-allopyran osyloxy)-2-cyclopentene-1-carbonitrile, using one- and two dimensional NMR spectroscopy, selective acid-catalysed cleavage of the glycosidic linkage of 6-deoxy-D-allose, and optical rotation data.

Carbohydrate Sequence↗
PubMed1980

The stability of 13,14-dihydro-15 keto-PGE2.

13,14-Dihydro-15 keto-PGE2 decomposes by first order reaction kinetics, dependent on pH, temperature and albumin concentration. Under common experimental conditions at or near neutrality in the absence of albumin decomposition is suspended with the formation of 13,14-dihydro-15-keto-PGA2. Cyclization into 11-deoxy-13,14-dihydro-15 keto-11,16-bicyclo-PGE2 occurs at elevated pH in purely aqueous buffers, and also at or near neutrality in the presence of albumin. Albumin accelerates, quantitatively, the decomposition of 13,14-dihydro-15 keto-PGE2 and promotes, qualitatively, the formation of the bicyclo rearrangement product. High performance liquid chromatographic analysis indicates that the cyclization product exists in at least three epimerically distinct forms. The two major epimers have been synthesized and isolated in pure form. They differ, mainly, by their optical rotation.

Albumins↗
PubMed1984

The reversible deactivation of beta-lactamase from Staphylococcus aureus by quinacillin and cephaloridine and its modification by antibodies.

The effect of antibody on the reversible deactivation of the beta-lactamase (penicillin amino-beta-lactamhydrolase, EC 3.5.2.6) from Staphylococcus aureus has been studied using quinacillin and cephaloridine as substrates. The latter has been shown to exhibit the characteristics of an A-type substrate Citri, N., Samuni, A. and Zyk, N. (1976) Proc. Natl. Acad. Sci. U.S.A. 73, 1048-1052) and reversibly to lower the activity of the enzyme towards benzylpenicillin in a manner analogous to quinacillin. Both divalent and monovalent antibodies reduce the activity of the lactamase to 60% of the native value in the absence of substrate. The reduction by monovalent antibody is slow (t1/2 approximately equal to 25 min). Both divalent and monovalent antibodies modify the time-course of reversible deactivation independently of being added before or subsequent to deactivation by substrate. The full recovery of activity is delayed in the case of quinacillin and accelerated for cephaloridine. The activity against benzylpenicillin in the deactivated states is unaffected. These effects are shown to reflect the changed rates of hydrolysis of the two substrates in the presence of antibody. The effect of antibody is mediated by minor conformational change. Continuous assays for following the hydrolysis of quinacillin and cephaloridine by optical rotation are reported.

Cephaloridine↗
PubMed1981

Bombesin analogs: effects on thermoregulation and glucose metabolism.

Twenty-six peptides, analogs of bombesin (BNa) and gastrin releasing peptide (GRP), have been synthesized by the solid phase method. The synthetic peptides were purified by ion exchange and partition chromatography and shown to be homogenous under various conditions on RP-HPLC. They were further characterized by TLC, amino acid analysis and optical rotation. These peptides have been administered IC to rats and their effects on thermoregulation and glucoregulation have been compared to those of the two natural peptides: frog skin bombesin (BNa) and GRP. Their structure activity relationship is also discussed. The minimum essential residues required for full potency of bombesin-like effects is represented by an acetylated C-terminal 8-peptide fragment, where in position 7 of this peptide an L-amino acid such as alanine, histidine or glutamine, or the D-glutamine residue can be introduced. Modification of the tryptophan [8] and histidine [12] residues by alanine abolished the biological potency of those peptides. Analogs with a free N-terminus were found to express little, but significant, activity, thus indicating that blocked N-terminus is necessary for maximal response. [Ac-Ala7, DAla11]-bombesin (7--14) and [Ac-DGln7 DAla11]-bombesin (7--14) were found to be more potent than bombesin, whereas [Ac-DAla7, DAla11]-bombesin or [Ac-DAla7, DAla11] bombesin N-methylamide were found to have 10 and 1% of bombesin potency, respectively.

Amino Acid Sequence↗
PubMed1988

Reversal in helix sense of copoly(beta-alkyl-L-aspartate-beta-benzyl-L-aspartate).

The conformation of copoly(beta-alkyl-L-aspartate-beta-benzyl-L-aspartate), in which the alkyl group is ethyl, propyl, butyl, hexyl, nonyl, dodecyl, or stearyl, was studied in solution and the solid state by optical rotatory dispersion and circular dichroism methods. The helix sense of the copolyaspartate studied here is transformed from a left-handed to right-handed alpha-helix as the degree of alkylation increases. Reversal in helix sense occurs, i.e., the left-handed alpha-helix based on the handedness of poly(beta-benzyl-L-aspartate) is transformed into a right-handed alpha-helix with increase in alkyl groups with right-handed nature. Reversal in helix sense is also observed for copolyaspartates with an intermediate or high degree of alkylation as temperature rises. Copolyaspartates with hexyl, nonyl, or dodecyl groups exhibit an induced circular dichroism around 230-238 nm and can form an ordered side chain structure which is broken down at high temperature. One has to consider the conformation of the omega-helix and beta-form of the copolyaspartates in the solid state in addition to the reversal in helix sense. Copolyaspartates with a low degree of alkylation are in the alpha-helical conformation over the low temperature range and adopt the omega-helical conformation in the high temperature range, indicative of a thermal alpha-omega transition. A small number of alkyl groups can be incorporated into the benzene ring stacking of the omega-helix, but not a large number. All the copolyaspartates can assume the beta-form at high temperatures. The helix conformation is not significantly affected by the formation of side chain crystals of the copolyaspartate with a large number of stearyl groups, in contrast to copolyglutamate.

Circular Dichroism↗
PubMed1979

Isolation and identification of S(+)-3-hydroxyisobutyric acid in the urine of rats loaded with isobutyric acid.

3-Hydroxyisobutyric acid has been isolated from the urine of rats loaded with sodium isobutyrate. An optical rotation measurement of the methyl ester derivative shows this compound to be the S(+) stereoisomer. This is the same stereoisomer that has been previously identified in cultures of bacteria incubated with ammonium isobutyrate (Aberhart, D.J. (1977) Bioorg. Chem. 6, 191--201).

Animals↗
PubMed1990

Laser-based detectors in chromatographic analysis.

Advances in detection technology have been a vital part of the development of microscale chromatographic techniques. Separation techniques such as microbore liquid chromatography impose severe constraints on the permissible volume of detector cells. The use of lasers to construct a new generation of chromatographic detectors has satisfied the need for low volume detection and high sensitivity. The unique properties of laser radiation have been used to advantage in designing new approaches to the detection of optical absorbance through fluorescence emission and thermal effects. New approaches to monitoring refractive index changes and optical rotation have also been developed. Together, the combination of microscale-separation techniques and highly sensitive detection provide a powerful tool for analysing small quantities of samples. Yet, there are practical limitations arising from the cost and complexity of much of the instrumentation reported to date, as well as the difficulties of preparing small samples for analysis which have limited the wide-scale application of these methods to solve practical problems. Recent advances in laser technology such as the advent of diode lasers may be useful in overcoming some of these limitations.

Chromatography↗
PubMed1988

A glycopeptide from adenocarcinoma tissue of human lung.

A glycopeptide from adenocarcinoma tissue of human lung was extracted by protein digestion with papain (EC 3.4.22.2) and trypsin (EC 3.4.21.4). This component was isolated by Pevikon block electrophoresis. It possessed hexose, glucosamine, fucose, galactosamine, and sialic acid. In its carbohydrate composition and also the abundance of threonin in the peptide moiety it was quite similar to the glycoprotein from gastrointestinal tract. The physical characteristic of the two, such as their optical rotation and viscosity, were also very similar each other.

Adenocarcinoma↗
PubMed2005

Ginkgolides and bilobalide: their physical, chromatographic and spectroscopic properties.

Ginkgolides A, B, C, J, K, L and M and bilobalide are rare terpene trilactones that have been isolated from leaves and root bark of the Chinese tree Ginkgo biloba. The structures of the highly oxidized ginkgolides were independently elucidated in the 1960s by the groups of Nakanishi and Sakabe. Later these compounds were found to be potent and selective antagonists of platelet activating factor, which fact triggered much new research. During the past 40 years, much physical, chromatographic and spectroscopic data have been published on these compounds in various, sometimes inaccessible, sources. The published melting points, solubility in different solvents, ionization constants, chromatographic behaviour, specific optical rotations, UV, IR, MS and NMR data, and X-ray studies are summarized and, where necessary, discussed. The literature until April 2005 has been reviewed.

Chromatography, Gas↗
PubMed2004

Vibrational circular dichroism spectra of protein films: thermal denaturation of bovine serum albumin.

Vibrational circular dichroism (VCD) spectroscopy has been used for the first time to investigate the thermal denaturation of proteins in H(2)O solutions. Films prepared from heated aqueous solutions were used for these investigations. A well-known alpha-helical protein, bovine serum albumin (BSA), is used for this first study. Both VCD and infrared absorption results obtained for BSA films indicate that the heat treatment of BSA induces significant amounts of beta-sheet structure and that the denaturation process is irreversible. To verify the irreversible nature of thermal denaturation, optical rotation was also measured as a function of temperature in both heating and cooling cycles. These results also indicate that thermal denaturation of BSA in solution is irreversible. This study establishes the usefulness of films for VCD investigations and offers new avenues for VCD studies on biologically important systems.

Animals↗
PubMed2004

X-ray and conformational analysis of methyl 3-amino-2,3-dideoxy-alpha-D-arabino-hexopyranoside.

The structure, conformation and configuration of methyl 3-amino-2,3-dideoxy-alpha-d-arabino-hexopyranoside were confirmed by (1)H NMR, (13)C NMR and IR spectroscopy, as well as by optical rotation. The structure of the compound studied was also determined by single crystal X-ray crystallography at 293 K and refined to a final R=0.0521 based on 1798 independent reflections. The title compound crystallized in the tetragonal space group P4(3) with a=6.572(1) angstrom, b=6.572(1) angstrom, c=41.161(8) angstrom, D(c)=1.324 Mgcm(-3) and V=1777.8(5) angstrom(3) for Z=8. The packing arrangement in the unit cell displayed a stratified structure. Moreover, medium-strength N-H. . .O and O-H. . .O hydrogen bonds, which stabilized the 3-D structure of compound I, were observed.

Carbohydrate Conformation↗