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S H Koenig

Publications and source records attributed to S H Koenig.

At least 73 records · Page 4Linked to original sources
PubMed1987

Transverse relaxation of solvent protons induced by magnetized spheres: application to ferritin, erythrocytes, and magnetite.

Since 1/T2 of protons of tissue water is generally much greater than 1/T1 at typical imaging fields, small single-ion contrast agents--such as Gd(DTPA), which make comparable incremental contributions and therefore smaller fractional contributions to 1/T2 compared to 1/T1--are not as desirable for contrast-enhancement as agents that could enhance 1/T2 preferentially. In principle, such specialized agents will only be effective at higher fields because the field dependence (dispersion) of 1/T1 is such that it approaches zero at high fields whereas 1/T2 approaches a constant value. The residual 1/T2 is called the "secular" contribution and arises from fluctuations in time--as sensed by the protons of diffusing solvent or tissue water molecules--of the component of the magnetic field parallel to the static applied field. For solutions or suspensions of sufficiently large paramagnetic or ferromagnetic particles (greater than or equal to 250 A diameter), the paramagnetic contributions to the relaxation rates satisfy 1/T2 much greater than 1/T1 at typical imaging fields. We examine the theory of secular relaxation in some detail, particularly as it applies to systems relevant to magnetic resonance imaging, and then analyze the data for solutions, suspensions, or tissue containing ferritin, erythrocytes, agar-bound magnetite particles, and liver with low-density composite polymer-coated magnetite. In most cases we can explain the relaxation data, often quantitatively, in terms of the theory of relaxation of protons (water molecules) diffusing in the outer sphere environments of magnetized particles. The dipolar field produced by these particles has a strong spatial dependence, and its apparent fluctuations in time as seen by the diffusing protons produce spin transitions that contribute to both 1/T1 and /T2 comparably at low fields; for the larger particles, because of dispersion, the secular term dominates at fields of interest. On the basis of the agreement of theory with data for solutions of small paramagnetic complexes, large magnetite particles, and liver containing low-density polymer-coated magnetite agglomerates, it is argued that the theory is sufficiently reliable so that, e.g., for ferritin--for which 1/T2 is unexpectedly large--the source of its large relaxivity must reside in nonideal chemistry of the ferritin core. For blood, it appears that diffusion through intracellular gradients determines 1/T2.

Animals↗
PubMed1987

Modification of relaxation of lipid protons by molecular oxygen and nitroxides.

Measurement of proton 1/T1 in model lipids from 0.00023 to 1.3 Tesla, at 5 degrees C and 37 degrees C, shows that both oxygen and nitroxides effectively enhance the relaxation rates of the protons of lipids. Equilibration with 1 atm of oxygen has a sixfold greater effect on lipid protons than on water protons, primarily because of the high lipid solubility of oxygen. The maximum relative relaxivity of oxygen for lipid protons occurs at 0.12-0.8 Tesla. Lipid soluble nitroxides have a four- to eightfold greater effect on lipid protons than on water protons. This high relaxivity, combined with the high lipid solubility possible with nitroxides, could lead to significant contrast in vivo in lipid environments.

Cyclic N-Oxides↗
PubMed1986

Electron spin resonance and magnetic relaxation studies of gadolinium(III) complexes with human transferrin.

A human serum transferrin complex was prepared in which Gd(III) was substituted for Fe(III) at the two metal-binding sites. Characteristic changes upon metal binding in both the UV absorption of ligated tyrosines and the solvent proton longitudinal magnetic relaxation rates demonstrated 2/1 metal stoichiometry and pH-dependent binding constants. Binding studies were complicated both by binding of Gd(III) to nonspecific sites on transferrin at pH less than or equal to 7 and by complexation of the Gd(III) by the requisite bicarbonate anion at pH greater than or equal to 6.0. A unique Gd(III) electron spin resonance spectrum, with a prominent signal at g = 4.96, was observed for the specific Gd(III)-transferrin complex. The major features of this spectrum were fit successfully by a model Hamiltonian which utilized crystal field parameters similar to those determined for Fe(III) in transferrin [Aasa, R. (1970) J. Chem. Phys. 52, 3919-3924]. The magnetic field dependence of the solvent proton relaxation rate was measured as a function of both pH and metal ion concentration. An observed biphasic dependence of the relaxation rate on metal concentration is attributed to either sequential metal binding to the two iron-binding sites with different relaxation properties or random binding to two sites that are similar but show conformationally induced changes in relaxation properties as the second metal is bound. The increase in the solvent proton relaxation rate with pH is consistent with a model in which a proton of a second coordination sphere water molecule is hydrogen bonded to a metal ligand which becomes deprotonated at pH 8.5.

Binding Sites↗
PubMed1986

Magnetic field dependence of solvent proton relaxation rates induced by Gd3+ and Mn2+ complexes of various polyaza macrocyclic ligands: implications for NMR imaging.

The magnetic field dependence of the solvent water proton longitudinal relaxation rate 1/T1 (the NMRD profile) has been measured for solutions of chelates of Gd3+ and Mn2+ ions with two different polyaza macrocyclic ligands: 1,4,7-triazacyclononane-N,N',N",-triacetic acid (NOTA) and 1,4,7,10-tetraazacyclododecane-N,N',N",N'"-tetraacetic acid (DOTA). Studies were carried out mainly near physiological pH, but the pH dependence was also examined in some cases. The results are compared with published data for complexes of Gd3+ and Mn2+ ions with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). Competition experiments for the NOTA and DOTA chelates with EDTA and DTPA were also performed. It is found that, over the field range in which NMR imaging is currently being done, different symmetries of otherwise similar chemical ligands can alter 1/T1 of solvent protons by factors of up to three. The ligand environment can influence the relaxation times of the electronic spin moments of the ions, as well as their coordination number, thereby changing both the inner and outer sphere contributions to the relaxivities of the complexes. The relevance of these results to questions of efficiency and toxicity of these chelates as agents for enhancement of contrast in NMR images is discussed.

Animals↗
PubMed1986

1/T1 NMRD profiles of solutions of Mn2+ and Gd3+ protein-chelate conjugates.

Bovine immunoglobulins (IgG) and bovine serum albumin (BSA) were multiply labeled with multidentate ligands, either ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA), and metal ions were inserted to form the ternary protein-ligand-ion conjugates. The NMRD profiles (the magnetic field dependence of 1/T1) of solutions of the ternary conjugates differ greatly from those of the corresponding binary ligand-metal-ion complexes, both in magnitude and functional form, exhibiting 5- to 10-fold greater relaxivities and prominent peaks near 20 MHz. The inference is that the protein-bound chelates are relatively rigidly attached to the macromolecules. The structure and metal ion affinities of these novel conjugates, as well as the relevance to contrast enhancement in NMR imaging, is discussed.

Binding Sites↗
PubMed1986

Relaxometry of ferritin solutions and the influence of the Fe3+ core ions.

The magnetic field dependence of 1/T1 over the range 0.01 to 50 MHz proton Larmor frequency (NMRD profile) is reported for water protons in solutions of horse spleen apoferritin, and of ferritin reconstituted at both low and high iron levels. The apoferritin results are in every way typical of diamagnetic spherical proteins of their size (K. Hallenga and S. H. Koenig, Biochemistry 15, 4255 (1976)). Titration of up to 24 ferrous ions per protein molecule, with subsequent oxidation to ferric, shows a nonlinear saturating contribution to the NMRD profile which is interpreted as arising from a small number of ferric ions (six to eight) bound close to the outside of each ferritin molecule, and a comparable number of interior sites. The latter become multiply occupied as the core grows and do not contribute measurably to 1/T1 in this state. The former sites are never more than singly occupied, and their contribution to the solvent proton relaxation rates is independent of the loading of the core. Measurements of 1/T2 at 20 MHz are quite in accord with theoretical expectations for apoferritin and ferritin with up to 24 ferric ions per molecule. However, a marked increase in 1/T2 is observed at higher iron loadings that we are unable to account for within the framework of the theory of outer sphere relaxation, even when the effects arising from inhomogeneities in the local magnetic field are included. A sample of human spleen hemosiderin was found to have the same 1/T1 NMRD profile as a comparable sample of ferritin.

Animals↗
PubMed1986

Relaxation of water protons in the intra- and extracellular regions of blood containing Gd(DTPA).

The magnetic field dependence of the longitudinal relaxation rates 1/T1 (NMRD profiles) of blood and plasma from rabbits before and after injection of Gd(DTPA) are reported as a function of magnetic field strength from 0.01 to 50 MHz. Over 100 values along the time-dependent magnetization were recorded for each 1/T1 and analyzed for multiple exponentials. From these data, which indicate a single exponential, from the measured Gd content of each sample, and the NMRD profiles, we show that Gd is in the extracellular space only and is present as rotationally mobile Gd(DTPA), uncomplexed with protein or blood cells; and that the water protons exchange rapidly between the intra- and extracellular regions.

Animals↗
PubMed1986

Magnetic field dependence (NMRD profile) of 1/T1 of rabbit kidney medulla and urine after intravenous injection of Gd(DTPA).

The measurement of NMRD profiles of water protons of excised tissues containing paramagnetic metal ions is one of the few ways of determining the biochemical and biophysical state of these ions in vivo. It is of critical importance, for example, to verify that Gd, injected as Gd(DTPA) to enhance contrast in MRI, remains chelated, since free Gd ions are highly toxic. We have investigated this in the renal medulla of rabbits. Fitting the magnetization data at each field of the dispersion to a single exponential shows that Gd accumulates predominantly in the renal medulla, from which it is cleared within 18 hours, and that Gd(DTPA) introduced intravenously into rabbits is excreted as Gd(DTPA) in the urine as rotationally mobile as in neat water. Taking a larger data set at each field and fitting it to the sum of two exponentials, since the errors of the single exponential analysis were larger than for other tissues, shows that the relaxation behavior of the renal medulla, free of contrast agent, can be well-described by a single relaxation rate at 37 degrees C. For increasing concentrations of Gd in the medulla, as determined by ICP analysis, two relaxation rates are required to account for the data, due to compartmentalization of tissue water and inhomogeneous distribution of Gd. These results, and similar data after mild mechanical disruption of renal structures, show unequivocally that the Gd in the renal medulla remains the chelate complex Gd(DTPA) and rotationally mobile, for dosages up to 300 mumoles/kg injected.

Animals↗
PubMed1985

Magnetic relaxation of solvent protons by Cu2+- and VO2+-substituted transferrin: theoretical analysis and biochemical implications.

Measurements of the magnetic field dependence of the longitudinal nuclear magnetic relaxation rates of solvent protons (NMRD profiles) in solutions of paramagnetic proteins have contributed significantly to the elucidation of the physical biochemistry of a number of metalloprotein systems. In many cases, NMRD profiles were used as indicators of chemical state, both static and dynamic [cf. Brewer, C. F., Brown, R. D., III, & Koenig, S. H. (1983) J. Biomol. Struct. Dyn. 1, 961-997], in part because a proper theoretical description of the data, with realistic assumptions for a model system, was computationally intractable. This has been particularly true for Cu2+-protein complexes, attributable in part to the S = 1/2 ground-state configuration of the Cu2+ ions; significant progress in interpreting such data has been made only recently [Bertini, I., Briganti, F., Luchinat, C., Mancini, M., & Spina, G. (1985) J. Magn. Reson. 63, 41-55]. We report NMRD profiles for solutions of Cu2+ - and VO2+-substituted human transferrin, both S = 1/2 ions, as well as computations that include the effects of the anisotropic hyperfine interactions of the paramagnetic ions with their respective nuclei. The description of the data that results from these computations is quite good, sufficiently so that one can say with confidence that the protons that contribute to the relaxation are rather distant (approximately 3.5 A) from the ions and in rapid exchange (approximately 10(8) s-1) with solvent. A possible view, consistent with what is known of the biochemistry of these substituted transferrins, is that relaxation occurs in the second coordination sphere: the exchanging entity is a water molecule hydrogen bonded to a donor atom of the metal ion complex.

Copper↗
PubMed1985

Preparation and properties of metal ion derivatives of the lentil and pea lectins.

Lentil lectin (LcH) and pea lectin (PSA) belong to the class of D-glucose/D-mannose binding lectins and resemble concanavalin A (Con A) closely in physicochemical, structural, and biological properties. LcH and PSA, like Con A, are Ca2+-Mn2+ metalloproteins that require the metal ions for their saccharide binding and biological activities. Studies of the relationship between the metal ions binding and saccharide binding activity in LcH and PSA have been difficult due to the problem of metal ion replacement in these proteins. We now report a method of metal ion replacement in both lectins that allows substitution of the Mn2+ in the native proteins with a variety of transition metal ions, as well as substitution of the Ca2+ with Cd2+ in a particular complex. The following metal ion derivatives of both LcH and PSA have been prepared: Ca2+-Zn2+, Ca2+-Co2+, Ca2+-Ni2+, and Cd2+-Cd2+. All of these derivatives are as active as the native lectins, as demonstrated by precipitation with specific polysaccharides, saccharide inhibition of precipitation, and hemagglutination assays. The yields of these derivatives are good (generally greater than 70%), and the degree of metal ion incorporation is high (generally greater than 90%). The method of preparation is quite different from that for metal ion substitution in Con A, which proceeds via the apoprotein. In contrast, the apoproteins of LcH and PSA are unstable, aggregate above pH 4.0, and cannot be remetallized once formed.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1985

Proton and deuteron nuclear magnetic relaxation dispersion studies of Ca2+-Mn2+-concanavalin A: evidence for two classes of exchanging water molecules.

We have measured the magnetic field dependence of the nuclear magnetic relaxation rates (NMRD profiles) of solvent protons and deuterons in solutions of Ca2+-Mn2+-concanavalin A (Con A) with and without saccharide present. Data were obtained over the range -8 to 35 degrees C; the extension to the lowest temperature was made possible by the presence of 5 M salt. Since previous theoretical analyses, using accepted relaxation theories of 1H NMRD profiles alone, led to unsatisfactory conclusions, we have attempted to take advantage of the fact that the residence lifetime of a water ligand of the metal ions can influence the relaxation behavior of protons and deuterons differently. From a comparison of the present proton and deuteron results, we find that Ca2+-Mn2+-Con A has two classes of binding sites: one, associated with the inner coordiation sphere of the Mn2+ ions, having a resident lifetime for solvent water of approximately 10(-5) s that is reduced by the presence of saccharide and another having a lifetime of approximately 5 X 10(-9) s, located with the protons of the bound waters approximately 4.4 A from the Mn2+ ions (assuming two equivalent water molecules in this class), which is well beyond the coordination environment of the Mn2+ ions. The relaxation contribution of these more distant sites is unaffected by saccharide. The conclusions are corroborated by measurements of the temperature dependences of the proton NMRD profiles, which show quite clearly that the profiles are composite, containing two contributions with opposite dependences on temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1985

Proton and deuteron nuclear magnetic relaxation dispersion studies of Ca2+-Mn2+-lentil lectin and Ca2+-Mn2+-pea lectin: evidence for a site of solvent exchange in common with concanavalin A.

Measurements of the magnetic field dependence of the longitudinal magnetic relaxation rates (NMRD profiles) of solvent protons and deuterons led to the discovery of two classes of solvent binding sites in Ca2+-Mn2+-concanavalin A (CMPL) [Koenig, S. H., Brown, R. D., III, & Brewer, C. F. (1985) Biochemistry (second of three papers in this issue)]. In this paper, we compare proton and deuteron NMRD profiles of Ca2+-Mn2+-lentil lectin (CMLcH) and Ca2+-Mn2+-pea lectin (CMPSA) with those of CMPL. All three metalloproteins are D-mannose/D-glucose-specific lectins that have a high degree of structural similarity and require the metal ions for their biological activities. We have developed a method for the preparation of fully active metal ion derivatives of lentil lectin (LcH) and pea lectin (PSA), including the diamagnetic derivatives Ca2+-Zn2+-LcH and Ca2+-Zn2+-PSA [Bhattacharyya, L., Brewer, C. F., Brown, R. D., III, & Koenig, S. H.(1984) Biochem. Biophys. Res. Commun. 124, 857-862]. The behavior of these two lectins with regard to their NMRD profiles is essentially identical, for both the paramagnetic and diamagnetic forms. Together with CMPL, all three lectins have a common paramagnetic contribution with a negative temperature dependence of the rates, while CMPL contributes an additional component with a positive temperature dependence. The common contribution derives from the class of fast exchanging water molecules observed in the proton NMRD profile of CMPL (Koenig et al., 1985); their protons are calculated to be relatively remote from the Mn2+ ions (4.4 A for CMPL and 5.5 A for LcH and PSA).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1985

Comparison of the spectroscopic and saccharide binding properties of lentil and pea isolectins.

The lentil isolectins, CMLcH A and CMLcH B, and pea isolectins, CMPSA A and CMPSA B, are compared in terms of their spectroscopic and saccharide binding properties. The paramagnetic contribution to the solvent proton magnetic relaxation dispersion profiles of solutions of the isolectins of each protein are found to be essentially identical. Electron paramagnetic resonance spectra suggest a high degree of octahedral symmetry at the Mn2+ site for both pairs of isolectins. The near-ultraviolet absorption spectra of CMLcH A and CMLcH B are identical, as are the spectra of CMPSA A and CMPSA B. Carbohydrate binding activities of the isolectins of each protein are compared using hemagglutination, precipitation, and precipitation-inhibition assays, and are found to be identical, although the activities of CMLcH and CMPSA differ somewhat. These results demonstrate that the spectroscopic and saccharide binding properties of the isolectins of CMLcH are essentially identical, as are those of the isolectins of CMPSA, and suggest that native mixtures of the isolectins may be treated as single proteins in further studies.

Disaccharides↗
PubMed1985

Interactions of concanavalin A with a trimannosyl oligosaccharide fragment of complex and high mannose type glycopeptides.

It has previously been reported that the binding interactions of concanavalin A with a purified high mannose type glycopeptide from ovalbumin differs from that with simple mono- and oligosaccharides (Brewer, C.F. (1979) Biochem. Biophys. Res. Commun. 90, 117-122). We now report studies with a synthetic analog of complex type glycopeptides, and a synthetic trimannosyl oligosaccharide fragment that is common to both complex and high mannose type glycopeptides. We find that both synthetic oligosacchardes undergo similar interactions with concanavalin A which mimic the effects of binding corresponding larger glycopeptides. Furthermore, the relative affinity of the trimannosyl oligosaccharide is 130-fold greater than the binding of methyl-alpha-D-mannopyranoside. The results indicate that the trimannosyl oligosaccharide is a unique structural element recognized by the lectin.

Concanavalin A↗
PubMed1985

Magnetic field dependence of proton relaxation rates in tissue with added Mn2+: rabbit liver and kidney.

Since contrast in magnetic resonance imaging (MRI) is so sensitive to the magnetic relaxation rates of tissue protons, the use of paramagnetic ions to alter contrast in a tissue-specific fashion is an alluring prospect. The influence of these ions on the proton relaxation rates in homogeneous solutions is known to vary dramatically according to whether the ions are present as hydrated aquoions, in solute chelate, or immobilized in macromolecules. In tissue, there is the additional complication of access of water to the ions. In the present study, Mn2+ ions were introduced into rabbits both orally and intravenously in various chemical complexes. Accumulation of these ions in rabbit liver is demonstrated here, qualitatively, by MRI. The quantitation of the change in relaxation rates is investigated in excised samples of liver and kidney by study of the magnetic field dependence (dispersion) of the relaxation rates of the protons (NMRD profiles) of tissue water. Results are presented for several sets of experiments, including dose-response data for weakly chelated Mn2+ and time-response data for free and complexed Mn2+. The general findings are that, for liver, the response (the increment in the NMRD profile) is relatively rapid (less than 2 m); that it is relatively independent of how, or in what form, the Mn2+ is introduced; that it persists for several hours (at least); and that it saturates with increasing body load of Mn2+. Moreover, from the form of the NMRD profiles of liver, it is clear that the Mn2+ ions are bound irrotationally, perhaps to cell membrane, and, when introduced in chelated form, can become separated even from strongly associated chelate complexes. For kidney, the results are qualitatively similar, though different in detail.

Animals↗
PubMed1985

Magnetic field dependence of solvent proton relaxation in aqueous solutions of Fe3+ complexes.

It might appear that the Fe3+ ion would be particularly useful as an agent for enhancing contrast in NMR images since it has a relatively large magnetic moment and occurs in vivo in a variety of forms. Moreover, the concentration of Fe3+ changes locally in certain disease states (e.g., beta-thalassemia) and in trauma (formation of methemoglobin), and can be altered in the gastrointestinal tract by the ingestion of readily available dietary supplements. However, the Fe3+ ion is insoluble above pH approximately 4, and soluble chelate and protein complexes of Fe3+ tend to sequester the ions from solvent; hence, the efficacy of Fe3+ ions for relaxing water protons ought to be low under typical physiological conditions. We report the magnetic field dependence of the relaxation rate of solvent protons (NMRD profiles) for solutions of a variety of Fe3+ complexes to demonstrate the phenomenology relevant to NMR imaging. From these data we make some estimates to show that, despite the low relaxation rates of solvent protons in solutions of Fe3+ complexes, certain observed changes in image contrast are consistent, quantitatively, with inferences that can be drawn from solution data.

Contrast Media↗
PubMed1984

Preparation and characterization of Ca2+-Zn2+-derivatives of lentil and pea lectins and comparison with the native forms.

Ca2+-Zn2+-derivatives of lentil and pea lectins were prepared for the first time by a unique method involving dialysis of the native Ca2+-Mn2+-lectins against large excesses of metal ions in pH 4.0 buffer. Each derivative contained about 1.5 g atoms of Ca2+ and about 1 g atom of Zn2+ per monomer. The derivatives were found to be identical to their respective native forms, both in molecular weight and carbohydrate binding activities. Solvent proton relaxation dispersion measurements were used to characterize both the Ca2+-Zn2+- and Ca2+-Mn2+-complexes of the lentil lectin.

Calcium↗