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Biomedical subjects

J D Glickson

Publications and source records attributed to J D Glickson.

At least 109 records · Page 6Linked to original sources
PubMed1978

Inhibition of lysozyme by polyvalent metal ions.

The rate of hen egg-white lysozyme (mucopeptide N-acetylmuramoylhydrolase, EC 3.2.1.17), catalysis was determined in the presence of various metal ions (Co2+, Zn2+ and eight of the trivalent lanthanide ions). In the assay system employed, the lanthanides were found to inhibit more strongly than either Zn2+ or Co2+. The inhibition data was fitted to several models of the interactions of the metal ion with the enzyme. These models ranged in complexity from a single inhibitory metal binding site on the enzyme (two-parameter fit) to the presence of two non-independent and non-equivalent inhibitory metal binding sites (five-parameter fit). The more complicated models did not fit the data more precisely than the simplest one-site model, suggesting that the adoption of the simpler model is warranted. The fact that the association constants obtained from the simplest analysis for Co2+ (1.3 +/- 1.9 . 10(2) M-1) and Gd3+ (7.0 +/- 2.6 . 10(3) M-1) are consistent with literature values determined from spectroscopic measurements further supports the validity of the simplest model.

Cobalt↗
PubMed1978

An analysis of the Co2+-induced nuclear magnetic resonance perturbations of hen egg white lysozyme.

A general methodology is presented for analyzing dipolar shifts induced by paramagnetic ions in the nuclear magnetic resonance (NMR) spectra of ligand molecules. The method is applied to the shift perturbations induced by Co2+ in the spectrum of hen egg white lysozyme. A hypothesis testing scheme is employed to evaluate statistically the relative precision with which the axially symmetric and non-axially symmetric forms of the dipolar shift equation fit the observed data. The assumption of axial symmetry for the magnetic susceptibility tensor of Co2+ is rejected at the confidence level of 99%. Since the results presented here are similar to those reached in our analysis of lanthanide-induced shifts, we suggest that the assumption of axial symmetry may, in general, not hold. Similar conclusions have been reached by other investigators in studies of paramagnetic metal binding to model systems. We have included the three Co2+ coordinates in an eight-parameter fit of the Co2+ shift data. The Co2+ position obtained from this fit is in statistical agreement with the position inferred from x-ray data. Thus, the analysis of shift data may furnish a means for determining the site of metal complexation in macromolecules whose structure has been determined by x-ray crystallography.

Animals↗
PubMed1978

The interactions of gallium with various buffers and chelating agents in aqueous solution: gallium-71 and hydrogen-1 NMR studies.

The interactions of gallium (Ga) with the ligands, EDTA, NTA, phosphate, lactate, MOPS, TRIS and HEPES are investigated using both 71Ga and 1H nmr measurements. Both EDTA and NTA form strong complexes with gallium, which have a 1:1 stoichiometry. In alkaline solution the tetrahedral Ga(OD)4- competes strongly with EDTA in complex formation. In the lactate complex, there are probably three lactates per gallium present. The phosphate complexes of gallium are difficult to characterize on the basis of this investigation. The buffers, MOPS, TRIS, and HEPES, do not interact with gallium significantly. The ability of the ligands to bind gallium correlates well with their ability to inhibit gallium incorporation by L1210 leukemic cells.

Buffers↗
PubMed1978

A fluorescence study of the binding of calcium and terbium ions to angiotensin.

The interactions of angiotensin II and a synthetic analogue, [Asn1, Val5] angiotensin II, with Ca2+ and Tb3+ have been monitored using the intrinsic fluorescence of the tyrosine residue at position 4 in both molecules. The data indicate that angiotensin II binds both metals with a dissociation constant of approximately 1 X 10(-4) M-1, while no significant binding was observed with the amide analogue. This suggests that the side chain carboxyl group of aspartic acid forms part of the binding site. Since the value of the dissociation constant suggests chelation of the metals by the hormone, the terminal carboxyl group of the peptide is also probably involved in metal binding. The fact that energy transfer was observed between Tb3+ and the tyrosine of angiotensin places the hydroxl or carbonyl group of the tyrosine close to the metal binding site.

Angiotensin II↗
PubMed1978

Solution conformation of peptides by the intramolecular nuclear Overhauser effect experiment. Study of valinomycin-K+.

This study demonstrates how the intramolecular nuclear Overhauser effect (NOE) experiment can be employed quantitatively to select from a set of possible conformations for a peptide or a protein the particular conformation (or a group of conformations) most consistent with the data. This procedure is demonstrated on a model depsipeptide system--valinomycin K+ in CDCl3--for which the solution conformation has been inferred by other methods. The NOE enhancements are very sensitive to the conformations assumed by this antibiotic. It is shown that the set of conformations, collectively labeled as A2 (including the X-ray crystallographic structure) gives a very good description of the NOE enhancements. The structure proposed by Bystrov et al. (1977. Eur. J. Biochem. 78:63) for the uncomplexed valinomycin in nonpolar solvents is also consistent with the experimental data on the potassium complex. Using statistical hypothesis testing involving the Hamilton R-factor ratio criterion, all the other models have been rejected as inconsistent with the experimental data. A general formalism is presented for describing the NOE effects in isotropically reorienting molecules. The formalism is not restricted to the extreme narrowing limit of the rotational correlation times and hence applies to both small and large molecules. Some of the factors that can influence the NOE measurements, viz. anisotropic rotational diffusion, conformational averaging, and nuclear spin diffusion, have been considered in this study.

Magnetic Resonance Spectroscopy↗
PubMed1977

Nuclear magnetic resonance studies of the denaturation of ubiquitin.

The effects of pH, temperature and guanidine hydrochloride concentration on the structure of ubiquitin, a polypeptide which can activate adenylate cyclase and can mimic thymopoietin induced differentiation of prothymocytes, were monitored using nuclear magnetic resonance spectroscopy. This relatively small polypeptide (molecular weight of 8541) exhibits a remarkable stability towards pH and temperature changes. At 7 M guanidine hydrochloride concentration, the structure of ubiquitin is essentially a random coil.

Guanidines↗
PubMed1977

Proton nuclear magnetic resonances study of bleomycin in aqueous solution. Assignment of resonances.

The 1H NMR spectrum of the glycopeptide antineoplastic antibiotic bleomycin has been examined in D2O solution (Fourier transform nuclear magnetic resonance, 270 MHZ) and in H2O solution (correlation nuclear magnetic resonance, 250 MHZ). Resonances have been assigned to specific hydrogens of the two most abundant congeners, bleomycin-A2 (BLM-A2) and bleomycin-B2 (BLM-B2), on the basis of (1) homonuclear spin decoupling, (2) comparison of the spectra of BLM-A2, BLM-B2, fragments of these antibiotics, and the related antibiotic phleomycin, and (3) the pH dependence of chemical shifts. Resonance assignments are presented for all the CH protons of BLM-A2 and BLM-B2 except for the saccharide groups, for which only the anomeric proton assignments are given. All of the NH protons have been identified with specific resonances except for the two primary amide groups, which yield four well-resolved peaks, whose specific assignment was not attempted. This study serves as a basis for future investigations of the conformation of bleomycin and its interaction with metals and nucleic acids.

Bleomycin↗
PubMed1976

Intramolecular 1H nuclear Overhauser effect study of the solution conformation of valinomycin in dimethyl sulfoxide.

Determination of the mechanism of intramolecular nuclear Overhauser effects (NOE) in peptides and depsipeptides is essential to the use of this technique in conformational analysis of these and related biomolecules. Towards this end, 1H NMR double-resonance studies were conducted on valinomycin in (CD3)2SO at 90 MGZ (FT mode) and 250 MGZ (correlation mode). The NOE's are positive at the lower frequency and negative at the higher frequency. Consideration of the theoretical dependence of the NOE on the proton-proton internuclear correlation time and on the resonance frequency indicates that these results are explained by a predominantly dipolar relaxation mechanism. It is demonstrated that exchange modulation of scalar coupling does not contribute significantly to the NOE. A formalism for the NOE's of loosely coupled spin systems is presented which takes into account the effects of high magnetic-field strengths and long correlation times. An approximate analysis of the NOE data assuming a single correlation time for the entire molecule and ignoring cross-relaxation effects was used to evaluate various models that have been proposed for the conformation of valinomycin. The III-1 model of Patel and Tonelli (Patel, D.J., and Tonelli, A.E. (1973), Biochemistry 12, 486) fits the NOE and peptide NHCalphaH coupling constant data and is probably a preferred orientation in dimethyl sulfoxide. These experiments illustrate how intramolecular NOE data provide a valuable auxiliary method to other techniques for delineating the preferred solution conformation of peptides, depsipeptides, and other biomolecules.

Binding Sites↗
PubMed1976

1H nuclear magnetic resonance double resonance study of oxytocin in aqueous solution.

Peptide NH resonances in the 250 MHZ 1H nuclear magnetic resonance (NMR) spectrum of oxytocin in H2O were assigned to specific amino acid residues by the "underwater decoupling" technique (i.e., decoupling from corresponding CalphaH resonances, which are buried beneath the intense water peak). These experiments confirm previous assignments of A. I. Brewster an V. J. Hruby ((1973), Proc. Natl. Acad. Sci. U.S.A. 70, 3806) and A. F. Bradbury et al. ((1974), FEBS Lett. 42, 179). Three methods of assigning NH resonances of peptides--solvent titration, underwater decoupling, and isotopic labeling--are compared. As the solvet composition is gradually changed from dimethyl sulfoxide to H2O, oxytocin undergoes a conformational change at 70-90 mol % of H2O. Exposure to solvent of specific hydrogens of oxytocin in H2O was studied by monitoring intensity changes of solute resonances when the solvent peak was saturated. Positive nuclear Overhauser effects (NOE's) of 14 +/- 5 were observed for the Tyr ortho CH and meta CH resonances, respectively. Comparative studies with deamino-oxytocin indicate that these effects result predominantly from intermolecular dipoledipole interaction between aromatic side chain CH protons and protons of the solvent. The NOE's therefore indicate intimate contact between water and the aromatic CH hydrogens of the Tyr side chain. The extent of saturation transferred by proton exchange between water and NH group varies with Ph in a manner which appears to reflect the acid-base catalysis of the protolysis reaction. There is no indication that any NH protons are substantially shiedled from the solvent.

Magnetic Resonance Spectroscopy↗
PubMed1975

H nuclear magnetic resonance study of restricted internal rotation of N-6,N-6-dimethyladenine in aqueous solution.

Kinetics of internal rotation about the C(6)-N(6) bond of N-6,N-6-dimethyladenine (M2-6A) was investigated by -1H nuclear magnetic resonance line-shape analysis of the methyl resonances (220 MHz). Rates of rotation were determined for M2-6A deuterated at N(1) and for neutral M2-6A. Activation parameters for monodeuterated M2-6A at 22 degrees are Ea = 13.8kcal/mol, log A = 12.6, incrementG++=14.9 kcal/mol, incrementH++ = 13.1 kcal/mol, incrementS++ = minus 5.8 eu; for neutral M2-6A: Ea = 15.5 kcal/mol, log A = 14.9, incrementG++ = 12.6 kcal/mol, incrementH++ = 14.9 kcal/mol, incrementS++ =7.8 eu. Vertical stacking of bases interferes with internal rotation of the dimethylamino group.

Adenine↗
PubMed1975

Serum inhibition of in vitro 67Ga binding by L1210 leukemic cells.

The influence of human serum on in vitro 67Ga uptake by L1210 leukemic lymphoblasts has been investigated. Both high- and low-molecular-weight serum components inhibit cellular uptake of the isotope. Inhibition by the high-molecular-weight serum fraction correlates closely with the extent of binding of the radionuclide. Although transferring participates in high-molecular-weight inhibition, it accounts for 10 percent or less of the inhibitory and binding capacity. Similarly, various low-molecular-weight serum components, including citrate, phosphate, glutamate, and others, contribute to inhibition. This inhibition of 67Ca uptake by serum results from the presence of several, perhaps many, inhibitory components.

Animals↗
PubMed1975

Effect of growth rate and simian adenovirus-7 transformation on in vitro 67Ga binding to hamster embryo cells.

The influence of growth rate and malignant transformation on 67Ga uptake was studied using cultured hamster embryo fibroblasts. Normalnonconfluent cells in log phase of growth bound approximately twice as much isotope as did confluent cells in a plateau phase of growth. In contrast, cells transformed by simian adenovirus-7 (SA-7), WHICH WERE ALSO UNDERGOING LOG GROWTH, BOUND ALMOST NO 67Ga. These results suggest that, although the rate of cellular proliferation may influence tissue affinity for 67Ga, other factors must also be considered when studying the effect of malignant transformation.

Adenoviridae↗