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At least 37 records · Page 2Linked to original sources
PubMed1977

Interaction of hyperthermia and radiation: temperature coefficient of interaction.

Cell survival data were collected to determine the survival surface for asynchronous CHO cells X-irradiated at room temperature 100 min prior to a hyperthermic exposure. The survival surface could be approximately described by a survival model comprising three components of cell killing; the unperturbed radiation component, the unperturbed hyperthermia component and the interaction component. The temperature sensitivities of the hyperthermia component and of the interaction component were investigated by using different hyperthermic temperatures, revealing that the interacting component is significantly less sensitive to a change in temperature than the unperturbed hyperthermia component.

Cell Survival↗
PubMed1975

Elastin--proteoglycan interaction. Conformational changes of alpha-elastin induced by the interaction.

The interaction between alpha-elastin and a connective tissue proteoglycan was followed by optical density measurements and circular dichroism spectroscopy. It was found that interaction takes place at pH values below the isoelectric point of elastin with the formation of a complex coacervate. CD spectra demonstrated conformational changes of alpha-elastin caused by the interaction and resulting in an increase in the content of helical structure. This finding suggests the possibility of the involvement of proteoglycans in the molecular organization of elastin.

Circular Dichroism↗
PubMed1979

Interaction of metal ions with nucleic acids. Interaction of copper(II) with pyrimidine nucleosides and their derivatives.

1. In aqueous and non-aqueous solutions, copper(II) interacts with the N-3 of cytidine but not with the carbonyl group oxygens of pyrimidine nucleosides. 2. In aqueous solution, copper(II) interacts with the phosphate group and ribose of pyrimidine nucleotides, and additionally with N-3 of 5'-CMP. 3. Broadening of resonance signals of the H-5 proton of 5'-UMP and C-5 of 5'-UMP and 5'-TMP results probably from the interaction between metal ion and the phosphate group situated in direct vicinity of the above atoms. 4. In the copper(II)-pyrimidine nucleotide complexes in solid state, copper is coordinated with the phosphate group, and in 5'-CMP additionally with the pyrimidine moiety of the nucleotide.

Binding Sites↗
PubMed1979

[Interactions between macromolecular adjuvants and drugs. Part 16: Effects of human serum albumin and Mg2+ on oxytetracycline-polyvinylpyrrolidone interactions (author's transl)].

Equilibrium dialyses and fluorescent spectroscopic measurements demonstrated that human serum albumin (HSA) affects the oxytetracycline (OTC)--polyvinyl-pyrrolidone K 90 (PVP) interactions. The preferential binding of OTC with HSA, as compared to PVP, was evidenced by means of a three-compartment model. The binding values increased with the increase of the portion of PVP in the PVP-HSA mixture. Superadditive OTC bindings occurred at a ratio of 1:1 (by weight). The addition of Mg2+ to PVP-containing solutions, at a molar ratio of 1:1, also produced an increase of the interactions of this antibiotic with PVP, whereby maximal OTC-PVP bindings of 50--60% were reached.

Dialysis↗
PubMed1979

Interaction of rat muscle AMP deaminase with myosin. I. Biochemical study of the interaction of AMP deaminase and myosin in rat muscle.

AMP deaminase was completely solubilized from rat skeletal muscle with 50 mM Tris-HCl buffer (pH 7.0) containing KCl at a concentration of 0.3 M or more. The purified enzyme was found to be bound to rat muscle myosin or actomyosin, but not to F-actin at KCl concentrations of less than 0.3 M. Kinetic analysis indicated that 1 mol of AMP deaminase was bound to 3 mol of myosin and that the dissociation constant (Kd) of this binding was 0.06 micrometer. It was also shown that AMP deaminase from muscle interacted mainly with the light meromyosin portion of the myosin molecule. This finding differs from that of Ashby and coworkers on rabbit muscle AMP deaminase, probably due to a difference in the properties of rat and rabbit muscle AMP deaminase. AMP deaminase isozymes from rat liver, kidney and cardiac muscle did not interact with rat muscle myosin. The physiological significance of this binding of AMP deaminase to myosin is discussed.

AMP Deaminase↗
PubMed1978

RNA-RNA interactions in the binding site of protein L24 on 23S ribosomal RNA of E. coli. II. Sequence analysis of the interacting fragments.

A ribonucleoprotein complex containing several RNA subfragments from the 5' part of 23S RNA was recovered after digestion of the reconstituted complex between 23S RNA and protein L24. It was suggested in the preceding paper that the RNA subfragments 4B, 10A and 9, which are widely separated in the sequence, strongly interact. These subfragments were previously partially sequenced by the classical fingerprinting methods. Their sequences have now been completed with rapid new RNA sequencing methods. We propose here a base-pairing model showing how these subfragments may interact with one another.

Base Sequence↗
PubMed1978

Theoretical calculations of base-base interactions in nucleic acids: II. Stacking interactions in polynucleotides.

Base-base interactions were computed for single- and double stranded poly,ucleotides, for all possible base sequences. In each case, both right and left stacking arrangements are energetically possible. The preference of one over the other depends upon the base-sequence and the orientation of the bases with respect to helix-axis. Inverted stacking arrangement is also energetically possible for both single- and double-stranded polynucleotides. Finally, interacting energies of a regular duplex and the alternative structures were compared. It was found that the type II model is energetically more favourable than the rest.

Base Sequence↗
PubMed1975

Studies on human plasma C1 inactivator-enzyme interactions. I. Mechanisms of interaction with C1s, plasmin, and trypsin.

This study has explored the nature of the molecular events which occur when C1 inactivator, a human plasma inhibitor of the complement, kinin-forming, coagulation, and fibrinolytic enzyme systems, interacts with C1s, plasmin, and trypsin. Purified inhibitor preparations demonstrated two bands, when examined by acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). The molecular weights of the major and minor bands were 105,000 and 96,000 daltons, respectively. The minor component appeared to be immunologically and functionally identical to the main C1 inactivator component. Loss of C1s and plasmin functional activity was associated with the formation of a 1:1 molar complex between the inhibitor and each enzyme. These complexes were stable in the presence of SDS and urea. The light chain of both these enzymes provided the binding site for C1 inactivator. Complex formation and enzyme inhibition occurred only with native and not with an inhibitor preparation denatured by acid treatment, thereby demonstrating the importance of conformational factors in the enzyme-inhibitor reaction. Although peptide bond cleavage of the C1 inactivator molecule by C1s was not documented, plasmin was found to degrade the inhibitor with the production of several characteristic derivatives. At least one of these products retained the ability to complex with C1s and plasmin. Trypsin, which failed to form a complex with C1 inactivator, degraded the inhibitor in a limited and sequential manner with the production of nonfunctional derivatives one of which appeared structurally similar to a plasmin-induced product. These studies therefore, provide new information concerning the molecular interactions between C1 inactivator and several of the proteases which it inhibits.

Animals↗
PubMed1977

Patient participation in the patient-provider interaction: the effects of patient question asking on the quality of interaction, satisfaction and compliance.

The purpose of this study was to investigate the effectiveness, dynamics, and consequences of a health education intervention designed to increase patient question asking during the patient's medical visit. Data were collected at a Baltimore family and community health center which provides outpatient services to a low income, predominantly black and female population. The majority of the study participants were, in addition, elderly and chronically ill. A total of 294 patients and 3 providers took part in the study. The study design included random assignment of patients to experimental and placebo groups with two non-equivalent (non-randomized) control groups. Findings included: (1) The experimental group patients asked more direct questions and fewer indirect questions than did placebo group patients. (2) The experimental group patient-provider interaction was characterized by negative affect, anxiety, and anger, while the placebo group patient-provider interaction was characterized as mutually sympathetic. (3) The experimental group patients were less satisfied with care received in the clinic on the day of their visit than were placebo patients. (4) The experimental group patients demonstrated higher appointment-keeping ratios (an average number of appointments kept divided by an average number of appointments made) during a four-month prospective monitoring period.

Consumer Behavior↗
PubMed1979

Interactions of cartilage proteoglycans with hyaluronate. Inhibition of the interaction by modified oligomers of hyaluronate.

Oligomers of hyaluronic acid were prepared by digestion of hyaluronic acid from rooster combs with testicular hyaluronidase (hyaluronate 4-glycanohydrolase, EC 3.2.1.35), leech head hyaluronidase (hyaluronate 3-glycanohydrolase, EC 3.2.1.36), and with fungal hyaluronidase (hyaluronate lyase from Streptomyces hyalurolyticus). The oligomers were fractionated by gel permeation, using Sephadex G-50. Oligomers isolated after incubation of the hyaluronic acid with the testicular hyaluronidase were further modified. To prepare oligomers with N-acetylglucosamine at both ends, terminal nonreducing glucuronic acid residues were removed with beta-glucuronidase. Reducing terminal N-acetylglucosamine residues were removed by reaction under mildly alkaline conditions. The reducing terminal N-acetylglucosamine residues were also reduced with sodium borohydride to form N-acetylglucosaminitol. The potentials of the various oligosaccharides to bind to the proteoglycan from bovine nasal septum cartilage were estimated by determining their effectiveness as inhibitors of the proteoglycan-hyaluronate interaction. The present study shows that, to bind maximally to the proteoglycan, the hyaluronate oligosaccharide must be at least 10 sugar residues in length and be terminated at the nonreducing and reducing ends with a glucuronate residue and an N-acetylglucosamine residue, respectively. Sugar residues extended beyond this basic decasaccharide, do not interact with the hyaluronate binding site on the proteoglycan.

Animals↗
PubMed1979

The interaction of a tyrosyl residue and carboxyl groups in the specific interaction between Streptomyces subtilisin inhibitor and subtilisin BPN'. A chemical modification study.

An ultraviolet absorption difference spectrum that is typical of a change in ionization state (pKa 9.7 leads to greater than 11.5) of a tyrosyl residue has been observed on the binding between Streptomyces subtilisin inhibitor (SSI) and subtilisin BPN' [EC 3.4.21.14] at alkaline pH, ionic strength 0.1 M, at 25 degrees C (Inouye, K., Tonomura, B., and Hiromi, K., submitted). When the complex of SSI and subtilisin BPN' is formed at an ionic strength of 0.6 M and pH 9.70, the characteristic features of the protonation of a tyrosyl residue in the difference spectrum are diminished. These results suggest that the pKa-shift of a tyrosyl residue observed at alkaline pH and lower ionic strength results from an electrostatic interaction. Nitration of tyrosyl residues of SSI and of subtilisin BPN' was performed with tetranitromethane (TNM). By measurements of the difference spectra observed on the binding of the tyrosyl-residue-nitrated SSI and the native subtilisin BPN', and on the binding of the native SSI and the tyrosyl-residue-nitrated subtilisin BPN' and alkaline pH, the tyrosyl residue in question was shown to be one out of the five tyrosyl residues of pKa 9.7 of the enzyme. This tyrosyl residue was probably either Tyr 217 or Tyr 104 on the basis of the reactivities of tyrosyl residues of the enzyme with TNM and their locations on the enzyme molecule. Carboxyl groups of SSI were modified by covalently binding glycine methyl ester with the aid of water-soluble carbodiimide, in order to neutralize the negative charges on SSI. In the difference spectrum which was observed on the binding of subtilisin BPN' and the 5.3-carboxyl-group-modified SSI at alkaline pH, the characteristic features of the protonation of a tyrosyl residue were essentially lost, and the difference spectrum is rather similar to that observed on the binding of the native SSI and the enzyme at neutral pH. This phenomenon indicates that the pKa of a tyrosyl residue of the enzyme is shifted upwards by interaction with carboxyl group(s) of SSI on the formation of the enzyme-inhibitor complex.

Amino Acids↗
PubMed1978

Interaction of metal ions with nucleic acids. Interaction of copper(II) with inosine and its derivatives.

1. The interaction of copper(II) with inosine, 2'-deoxyinosine, 1-methylinosine, 7-deazainosine, 6-methoxypurine riboside and IMP was examined. 2. Copper binds with the purine base of the nucleosides, and in IMP also with the phosphate group. Non interaction with ribose hydroxyl groups was observed. 3. In non-aqueous medium, the main site of copper binding is N-7 of inosine and 1-methylinosine, and additionally N-1 in 6-methoxypurine riboside. 4. In aqueous medium, coordination of copper with N-1 and N-7 of inosine and IMP is pH-dependent. 5. Formation of either a five-membered copper chelate with N-7 and oxygen at C-6, or a four-membered chelate of the type C(6)-O-Cu-N(1), is rather unlikely. 6. The crystalline copper-IMP complex [Cu(C10H11O8N4P).(H2O)] contains presumably two copper atoms coordinated in different manner. The phosphate group and N-7, but not the carbonyl oxygen, participate in the complex formation.

Chemical Phenomena↗
PubMed1979

Interaction of troponin subunits. The interaction between the inhibitory and tropomyosin-binding subunits.

The interaction of troponin-I and troponin-T was demonstrated by circular dichroism and gel filtration. Troponin-I gives a negative circular dichroism band between 300 and 260 nm while troponin-T gives two weak positive bands, one at 290 nm and the other at 263 nm. When troponin-I and troponin-T were mixed, the complex produced a strong negative circular dichroism band with a maximum around 280 nm. This band was most intense with a molar ratio of troponin-T to troponin-I of 1:1. The intensity of the band was 2.4 times that expected from the separate components. The interaction was independent of salt concentration from 0.15 to 0.5 M KCl. Gel filtration on Sephacryl S-200 showed that a stable 1:1 complex was formed between troponin-T and troponin-I. When troponin-C was added to the complex of troponin-T.troponin-I; the reconstituted troponin had a circular dichroism spectrum identical to that of native troponin. The oxidation state of troponin-I was important in reconstituting troponin. Oxidized troponin-I produced less change in the near ultraviolet circular dichroism when added to troponin-T and the troponin-C than did reduced troponin-I. This showed the subunits were not assembled correctly with oxidized troponin-I. When the reconstituted complex was reduced, the circular dichroism was restored to that of native troponin. Troponin reconstituted with oxidized troponin-I did not confer calcium sensitivity on actomyosin ATPase; activity was restored by reducing the complex.

Circular Dichroism↗
PubMed1975

Drug-biomolecule interactions: mechanism of ligand interactions with carbonic anhydrase studied by magnetic resonance relaxation and rapid reaction methods.

Kinetcs of interaction between the metalloenzyme carbonic anhydrase and either monovalent anions or aromatic sulfonamides were examined by three distinct fast reaction techniques: stopped flow, equilibrium perturbation, and magentic resonance relaxation. By correlating spectroscopic data on conformational and ionization equilibria of the complex and free species with the reaction kinetics, a relatively complete description of the mechanism can be presented. A proton-dependent equilibrium between two coordination forms of the free enzyme can be demonstrated spectroscopically. Anions selectively combine with the form predominating at low pH. For a series of carboxylate ligands, formate and substituted acetates, anion association is found to be three orders of magnitude greater than similar ligand substitution processes known in inorganic chemistry. For sulfonamide association, the attacking species are the form of carbonic anhydrase predominating at high pH and the neutral sulfonamide. Combination involving the neutral species is followed by loss of a proton to form the sulfonamido anion in the stabilized complex. This obligate proton transfer offers a probable explanation for the unique specificity of sulfonamides in inhibiting this enzyme. The anionic sulfonamido moiety can be shown to resemble closely a transition intermediate in the catalytic step of substrate hydration.

Acetates↗
PubMed1978

Thyroxine-protein interactions. Binding constants for interaction of thyroxine analogues with the thyroxine binding site on human thyroxine-binding globulin.

The binding constants for interaction of various thryoxine analogues with the thyroxine binding site on human thyroxine-binding globulin have been determined. Equilibrium dialysis, at pH 7.4 and 37 degrees C, was used to measure the competitive effects of different iodothyronine compounds on the binding of 125I-labeled thyroxine to highly purified thyroxine-binding globulin. Relative to L-thyroxine, K = 6 . 10(9) M-1, the association constants of some important analogues were D-thyroxine, 1.04 . 10(9) M-1, 3,5-diiodo-3'-isopropyl-L-thyronine, 4.9 . 10(8) M-1; L-triiodothyronine, 3.3 . 10(8) M-1, 3,3',5'-DL-triiodothyronine (reverse triiodothyronine), 3.1. 10(8) M-1; tetraiodothyropropionic acid, 2.7 . 10(8) M-1; tetraiodothyroacetic acid, 2.6 . 10(8) M-1; 3', 5'- diiodo-DL-thyronine, 8.3 . 10(7) M-1; and 3,5-diiodo-DL-thyronine, 7.1 . 10(7) M-1. Calculation of the deltaG0 values for binding of the analogues indicates that a major contribution to the free energy favoring binding is made by the alanine side chain of thyroxine. A change in configuration of the alpha-amino group from the L to D form causes an unfavorable change of 1 kcal/mol in the free energy of binding. Removal of the alpha-amino group as in tetraiodothyropropionic acid causes an unfavorable change of 1.9 kcal/mol in the free energy of binding. With regard to ring substituents, the results indicate that the two inner 3,5-iodines make about the same contribution to binding as the two outer 3', 5'-iodines.

Binding Sites↗
PubMed1979

Interaction of phenosafranine with nucleic acids and model polyphosphates. III. Heterogeneity in phenosafranine interactions with DNA base pairs.

Fluorescence and circular dichroism spectral measurements, thermal denaturation studies and binding competition experiments with netropsin and actinomycin D were carried out in systems containing phenosafranine bound to DNA's differing in base composition. The investigated properties exhibit a heterogeneity related to the content of A.T and G.C pairs in DNA and to the nature of phenosafranine binding modes. At low level of saturation of binding sites (r less than 0.1) phenosafranine does not show strong preference for any of the DNA base pairs in the overall binding. However, the strong monomer non-cooperative binding outside the helix (mode I1) occurs predominantly, even though not exclusively in G.C rich regions. The strong binding modes involving intercalated dye molecules (mode I2 and eventually mode II1) prevail in A.T rich regions. These binding modes become the principal types of strong phenosafranine interaction with DNA when the level of saturation of binding sites increases, i.e. at r greater than 0.1.20

Bacillus cereus↗
PubMed1979

Androgen-uterine interactions: an assessment of androgen interaction with the testosterone- and estrogen-receptor systems and stimulation of uterine growth and progesterone-receptor synthesis.

This study investigates growth and the induction of progesterone-receptor synthesis in the immature (day 20--23) rat uterus after injection of different doses of 5 alpha-dihydrotestosterone (DHT) and testosterone (T) in long- and short acting injection vehicles. Moderate doses of T (300 microgram/day in saline for 3 days) elicit uterine growth (ca. 250% of control) that is abolished by concomitant injections of antiandrogen (1 mg flutamide/day or 8 mg DIMP/day) but is unaffected by injections of antiestrogens (60 microgram CI-628 or U11,100A/day). Uterine growth evoked by 17 beta-estradiol (3 microgram/day for 3 days) is, however, only antagonized with the antiestrogens but not antiandrogens. Experiments employing whole uteri in vitro indicate that the specific nuclear uptake of 10(-8) M [3H]T is markedly inhibited by the antiandrogens DIMP, flutamide, and the hydroxylated flutamide metabolite (LACT) [LACT greater than DIMP greater than FLUT] while the antiestrogens CI-628 and U11,100A are ineffective. In contrast, the specific nuclear uptake of 10(-8) M [3H]-estradiol is inhibited by only the antiestrogens and not antiandrogens. When very high (5 or 10 mg) doses of DHT Are administered in an oil-containing injection vehicle, nuclear translocation and cytoplasmic depletion of the estrogen receptor does occur and a uterotrophic response is elicited which is resistant to antagonism by antiandrogen. Likewise, the DHT-stimulated increase in progesterone-receptor content is not decreased by concomitant antiandrogen. Similar 5 or 10 mg doses of DHT, administered in a water-soluble dimethylsulfoxide vehicle, show little estrogen-receptor movement and the DHT-induced uterine growth and induction of progesterone-receptor synthesis is almost completely eliminated with antiandrogen. Regardless of the degree of uterine growth stimulation, however, the androgens are poor stimulators of uterine progesterone-receptor synthesis compared with estradiol. These results indicate that androgens may interact with both the androgen- and estrogen-receptor systems in the uterus in inducing uterine growth and that the nature of the cellular mechanism, i.e., whether the androgen- and/or estrogen-receptor system is involved, is dependent critically upon the in vivo dose of androgen and the mode of hormone administration.

Androgen Antagonists↗