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PubMed1989

Evidence that the antimalarial activity of artemisinin is not mediated via intercalation with nucleotides.

The interaction of artemisinin, a new sesquiterpine lactone antimalarial drug, with some target macromolecules represented by calf thymus deoxyribonucleic acid (DNA) and the dinucleotide guanylyl (3----5) cytidine (GpC) was studied by 1H-NMR. There was no intercalation between artemisinin and DNA or GpC as judged by the lack in change of chemical shifts (delta delta) or coupling constants (delta J) of the C-13, C-14, and C-15 methyl groups of artemisinin. This conclusion was substantiated by studying the optical rotatory dispersion (ORD) between artemisinin and these target macromolecules. It is suggested that artemisinin exerts its antimalarial action via a mechanism different from that of the aminoquinolines antimalarial agents, possibly through the peroxygen linkage which is essential for artemisinin biological activity.

Acrylates↗
PubMed1975

Physiocochemical properties of a lipoprotein antigen of Echinococcus granulosus.

Molecular weight and optical properties of the lipoprotein B, the main antigen produced by the parasite in sheep hydatid fluid, have been determined. By sedimentation equilibrium studies, its molecular weight has been found equal to 120,000. Circular dichroism and optical rotatory dispersion spectra are consistent with an alpha-helix content of about 50%, and this ordered structure is not completely destroyed by dissociation in guanidinium choloride. The ORD spectrum is discussed in relation to the biological function of the lipoprotein antigen.

Animals↗
PubMed1981

Studies of peptide antibiotics. XLI. Syntheses of 6-L-valine-tyrocidine A and 7-L-ornithine-tyrocidine A.

Tyrocidine A (TA) is an antibiotic cyclic decapeptide with the sequence of cyclo (-L-Val1-L-Orn2-L-Leu3-D-Phe4-L-Pro5-L-Phe6-D-Phe7-L-Asn8-L-Gln9-L-Tyr10-). Gramicidin S (GS) regarded as a homolog of TA is also a cyclic decapeptide with the sequence of cyclo (-L-Val1-L-Orn2-L-Leu3-D-Phe4-L-Pro5-L-Val5-L-Orn7-L-Leu8-D-Phe9-L-Pro10-). GS shows higher antibacterial activity, whereas TA exhibits inhibitory activity on the biosynthesis of RNA. Two analogs of TA, [L-Val6]-TA (12a) and [L-Orn7]-TA (12b), were synthesized by the conventional method in order to study the interrelationships between the two related antibiotics TA and GS. Antibacterial activities of 12a and TA are nearly the same, but the activity of 12b is significantly lower. The optical rotatory dispersion spectra of 12a, 12b, and TA showed a trough at 233 nm region; the troughs of 12a and TA are nearly the same in depth, but the trough of 12b is shallower. Relationships between structure and activity of 12a and 12b compared with TA and GS were discussed.

Amino Acid Sequence↗
PubMed1973

Physical and chemical properties of Trichoplusia ni granulosis virus granulin.

The protein solubilized from the proteinic crystalline structure surrounding the granulosis virus of Trichoplusia ni by use of a carbonate buffer (pH 10.7) gives a major component, as analyzed by ultracentrifugation, with a molecular weight of 180,000. This protein has heterogeneous subunit structure as demonstrated by estimates of molecular weights by use of gel electrophoresis, amino-, and carboxy-terminal analyses, and peptide mapping of enzyme digests of the protein. The amino acid composition shows that the protein is acidic with a high percentage of amino acids with hydrophobic side groups. Optical rotatory dispersion studies reveal the presence of beta-structure in the protein complex. The conversion of the beta-structure to alpha-helix with sodium lauryl sulfate and to a random coil state with strong alkaline treatment are observed.

Amino Acids↗
PubMed1975

Chemical modification of yeast 3-phosphoglycerate kinase.

Sulfhydryl reagents, as well as mild hydrogen peroxide oxidation, do not inhibit the activity of yeast phosphoglycerate kinase, indicating that the single thiol group and 3 methionine residues present in the enzyme are not essential for activity. Nitration of phosphoglycerate kinase by tetranitromethane inhibits the enzyme by reaction with a single tyrosine residue. Substrates provide partial protection against inactivation by nitration. Circular dichroism spectra indicate that no conformational changes occur upon nitration. However, perturbation of the microenvironment surrounding the aromatic amino acid residues, particularly tyrosine, was observed. The same perturbation was observed on addition of the substrate 3-phosphoglycerate kinase to native phosphoglycerate kinase. The role of lysine in the action of yeast phosphoglycerate kinase has been studied by modification with O-methylisourea, 2-methoxy-5-nitrotropone, and pyridoxal phosphate. Guanidination shows that there are lysines essential for phosphoglycerate kinase; extrapolation to zero activity indicates that there are three essential lysines as judged by nitrotroponylation and three essential lysines when the enzyme is reacted with pyridoxal phosphate. Substrates afford partial protection and extrapolation to total protection indicates that up to three lysines are protected by MgITP and one lysine by 3-phosphoglycerate. Spectrofluorescence and optical rotatory dispersion measurements show that there is no detectable conformational change for the guanidinated phosphoglycerate kinase and that there are slight changes in the spectra suggesting that there may be slight conformational changes for the nitrotroponylated and the pyridoxal phosphate-modified enzymes.

Amino Acid Sequence↗
PubMed1975

Properties and immunochemical reactivities of carboxy-modified human serum albumin.

Seven carboxy modified and four amino modified derivatives of human serum albumin have been prepared and studied by optical rotatory dispersion measurements, gel filtration, immunoelectrophoresis, immunodiffusion and by use of an ammonium sulphate technique. It is found that carboxy groups are of major importance for the maintenance of the structure and function of human serum albumin, and that carboxy modification has a much more profound effect than amino modification has to the same relative extent.

Ammonium Sulfate↗
PubMed1989

A review of the application of chiroptical methods to analytical chemistry.

The analytical applications of the two most important chiroptical methods, optical rotatory dispersions (ORD) and circular dichroism (CD), have been surveyed, emphasizing the methods corresponding to the profile of the Journal of Pharmaceutical and Biomedical Analysis. After a brief introduction of the ORD and CD methods, the advantages and drawbacks of the application of the two methods have been described, and compared, and the calibration of ORD and CD instruments have been given. The analytical applications have been divided as follows: the use of ORD and CD in identification studies, the direct determination of optically active substances, the determination of optically active compounds after chromophore group formation, determination of optically inactive substances via their products with optically active compounds. The difference chiroptical methods increasing the selectivity of measurements and the chiroptical titrations have been summarized. Stress has been laid on the applicability of selective chiroptical detectors (based on laser light, too) used in liquid chromatography and the future developments have been mentioned.

Circular Dichroism↗
PubMed1971

Physicochemical properties of vancomycin and iodovancomycin and their complexes with diacetyl-L-lysyl-D-alanyl-D-alanine.

Electrometric and spectrophotometric titrations showed vancomycin to contain groups having pK values of about 2.9, 7.2, 8.6, 9.6, 10.5 and 11.7. Of these the four last-named were phenolic. Titration above pH11 and below pH1 was irreversible and antibiotic potency was destroyed. Combination with the specific peptide diacetyl-l-lysyl-d-alanyl-d-alanine hindered the titration of the first three phenolic groups. Spectrophotometric titration of iodovancomycin showed that the phenolic group with pK 9.6 was the one iodinated. The stability of the vancomycin-peptide complex in the range pH1-13 showed that complex-formation occurred only when carboxyl groups were ionized and the phenolic groups were non-ionized. The complex was formed in concentrations of urea up to 8m, of potassium chloride up to 4m, of sodium dodecyl sulphate up to 1%, and at temperatures up to 60 degrees C. From titration curves, organic chlorine and iodine analysis, and combination with peptide, a minimum molecular weight for vancomycin of 1700-1800 was estimated. Optical-rotatory-dispersion and circular-dichroism experiments suggested that vancomycin has only limited conformational flexibility. Both vancomycin and its complexes with peptide exhibited properties suggesting aggregation. Vancomycin and iodovancomycin can be fractionated into a main fraction and at least three minor components. The isolation of these fractions salt-free is described and their antibiotic properties are shown to correlate with their ability to form complexes with peptide.

Alanine↗
PubMed1975

Conformational changes in the progesterone binding globulin-progesterone complex.

An improved purification procedure for the progesterone-binding globulin (PBG) of the pregnant guinea pig has been developed utilizing sulfopropyl Sephadex, a strong cation exchanger, in the first step. The method exploits the low pI (2.8) and favorable acid stability of the glycoprotein. Subsequent chromatographies on DEAE-cellulose and Sephadex G-200 afford a highly purified PBG that exhibits the previously observed polydispersity (R.M. Burton et al. (1974), Biochemistry 13, 3554-3561). Circular dichroism, optical rotatory dispersion, and difference uv spectra all indicate the purified protein to undergo a conformational transition upon forming a complex with a steroid ligand. The CD and ORD spectra cannot be interpreted in terms of tertiary structure probably due to carbohydrate contributions. However, the difference spectra indicate strong perturbation of both a tryptophan residue and the steroid chromophore in the complex.

Animals↗
PubMed1970

The structure of anticapsin, a new biologically active metabolite of Streptomyces griseoplanus.

1. Physical and analytical data obtained on crystalline anticapsin indicated the empirical formula C(9)H(13)NO(4). Spectral data (u.v., i.r. and proton magnetic resonance) and formation of l-tyrosine on hydrolysis revealed the functionalities and carbon skeleton of the new epoxy keto amino acid. 2. The optical properties of anticapsin (optical rotatory dispersion and circular dichroism) permitted assignment of absolute configuration to the new metabolite. 3. Treatment of anticapsin with hot methanolic hydrochloric acid followed by acetylation gave C(18)H(19)NO(5), the alpha-alkoxycyclohexenone derivative. Analysis of the nuclear-magnetic-resonance and mass spectra of the latter allowed its structure to be determined and confirmed the assigned structure of anticapsin.

Amino Acids↗
PubMed1983

Spectral studies of magnesium porphyrin--apomyoglobin and apohemoglobin complexes.

Complexes of magnesium protoporphyrin and magnesium mesoporphyrin with apomyoglobin and apohemoglobin have been prepared and studied by electronic, circular dichroism, and optical rotatory dispersion spectroscopy. The myoglobin complexes show prominent splittings and red shifts of the visible absorption bands, with respect to those for the hemoglobin analogs. Comparisons are made with other heme protein systems that display similar spectral features. Different reasons for the observations are considered, including multiple conformer formation, polarity effects of the protein environment, and the formation of six-coordinate magnesium species through H2O coordination for the Mb complexes (the latter explanation being favored).

Animals↗
PubMedDate not supplied

alpha and piDL helical states of alternating poly(gamma-benzyl D-L-glutamate) in solution.

As in solid state, strictly alternating poly(gamma-benzyl D-L-glutamate) in solution can adopt two different helical conformations. Besides the alpha helix, a second helical conformation is found at higher temperatures in dioxane and chloroform, the properties of which correspond to that of the piDL4 helix. As the molecules have a finite length a screw sense is favored for both helical forms thus giving rise to optical activity allowing the study of the transconformation by optical rotatory dispersion and circular dichroism besides infrared and dielectric measurements. Thus, as the temperature is raised the equilibria right-left handed alpha helices and alpha-piDL helical forms can be followed. The favored screw senses are determined by the number of interacting side chains for the alpha helix and by the number of hydrogen bonds which are formed in the piDL helical conformation. The side chain-side chain interactions in the alpha helix are experimentally shown to be attractive.

Glutamates↗
PubMed1968

Conformation of blood-group and virus receptor glycoproteins from red cells and secretions.

Optical rotatory dispersion of human blood-group and virus receptor glycoproteins from erythrocytes and secretions was studied in the far-ultraviolet. Erythrocyte membrane blood-group glycoproteins, with potent virus receptor activities, contained significant alpha-helical and extended beta conformations, whereas the glycoproteins of secretions were largely disordered. These conclusions were supported by determination of the Moffitt constants (b(0)) and by measurements of circular dichroism.

Antiviral Agents↗
PubMed1969

Solution properties of polygalacturonic acid.

1. The specimen of polygalacturonic acid used in these studies was shown to contain very little neutral sugar, methyl ester groups or ash, and only residues of galacturonic acid. Its electrophoretic homogeneity was examined in pyridine-acetic acid buffer at pH6.5 and in borate buffer at pH9.2. The distribution of effective particle weights was shown to be fairly narrow. 2. The pH-titration curve of the polymer gave a pK value of 3.7. 3. The interaction of the polymer with Ruthenium Red was studied and titration curves were obtained for the spectral shifts associated with the formation of a complex. 4. Optical-rotatory-dispersion studies showed that the Drude constant, lambda(c), was dependent on pH. 5. Polygalacturonic acid was shown to display non-Newtonian properties in solution and to have an anomalously high relative specific viscosity at low concentrations. 6. Studies were made of the pH-dependence of the sedimentation coefficient of the polymer. 7. These results are discussed in terms of the structure of the molecule and their relevance to the properties of pectic substances.

Buffers↗
PubMed1971

pH-dependent conformational changes of concanavalin A.

The pH dependence of the conformation of concanavalin A has been studied by means of optical rotatory dispersion and circular dichroism spectroscopy. At pH 2.9, 5.0, and 7.0, the major contribution to organized structure appears to be the beta conformation. At pH 9.1, the conformation of concanavalin A approaches the random coil or unordered form. No evidence could be found for the presence of any significant amount of alpha helix. The pH of maximum precipitin-like activity of concanavalin A is paralleled by the pH dependence of the parameter b(0) in the Moffitt equation.

Circular Dichroism↗
PubMed1979

Conformational changes accompanying the binding of antithrombin III to thrombin.

The conformational aspects of the binding of antithrombin III to thrombin were investigated by difference spectroscopy, circular dichroism, and optical rotatory dispersion. The CD and ORD studies indicate an increase of 6--8% in alpha-helix content at the expense of the beta structure, while the results from difference spectroscopy showed an increased exposure of approximately seven tyrosine residues. In the presence of heparin there is a slightly greater increase in helicity which is accompanied by exposure of an average of two tryptophan and one tyrosine residues. These spectral results indicate that the thrombin-antithrombin III complex formed in the presence of heparin differs in its conformation from that produced in its absence.

Antithrombin III↗
PubMed1969

Chemical modification of glutamate dehydrogenase by 2,4,6-trinitrobenzenesulphonic acid.

1. Modification with 2,4,6-trinitrobenzenesulphonic acid was studied for its effect on the structure, activity and response to regulatory effectors of ox liver glutamate dehydrogenase. 2. The modification affected amino groups only, and the relative reactivities of the amino groups of the enzyme are described. 3. A biphasic inactivation of the enzyme was observed and analysis of the course of inactivation and of modification showed that the rapid reaction of one amino group/subunit leads to loss of 80% of the enzymic activity. 4. NADH retarded the inactivation by 2,4,6-trinitrobenzenesulphonic acid, the protection increasing with NADH concentration. This, together with the previous observation, suggests that the rapidly reacting group is essential for the activity of the enzyme. 5. The effects of modification on the optical-rotatory-dispersion and sedimentation behaviour of the enzyme were studied. 6. The enzyme's response to the allosteric effector GTP was rapidly lost on modification, whereas its response to ADP was unaffected. Comparison of the inactivation and desensitization suggests that the reactive amino group is essential for both activity and GTP response, and that only a completely unmodified enzyme oligomer responds fully to GTP. 7. The merits of chemical-modification studies of large enzymes are discussed critically in connexion with the interpretation of these results.

Adenine Nucleotides↗
PubMed1968

Evidence for histidine in the active site of papain.

Papain was irreversibly inhibited by 1,3-dibromoacetone, a reagent designed to react first with the active-site cysteine residue and subsequently with a second nucleophile. The molecular weight of the inhibited enzyme was indistinguishable from that of papain itself, and no evidence of dimeric or oligomeric species was found. The optical-rotatory-dispersion curves of chloroacetone-inhibited papain and 1,3-dibromoacetone-inhibited papain were essentially similar. Amino acid analysis of the 1,3-dibromo[2-(14)C]acetone-inhibited enzyme and the performic acid-oxidized material clearly showed that a cysteine and histidine residue had been alkylated through the thiol and N-1 of the imidazole group respectively. These groups must therefore be within 5å of each other in the tertiary structure of papain. Possible mechanistic implications are briefly discussed.

Acetone↗