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PubMed1996

Conformation of manganese(II)-nucleotide complexes bound to rabbit muscle creatine kinase: 13C NMR measurements using [2-13C]ATP and [2-13C]ADP.

Conformations of cation-nucleotide complexes bound to rabbit muscle creatine kinase were investigated by measuring paramagnetic effects on 13C spin relaxation in E.Mn[2-13C]ATP and E.Mn[2-13C]ADP at three different frequencies, viz., 50, 75, and 125 MHz, and as a function of temperature in the range of 7-35 degrees C (at 75 MHz). Arrhenius plots of the temperature dependencies of relaxation rates show a positive slope with low activation energies of 1.3 +/- 0.2 kcal/mol and 2.0 +/- 0.2 kcal/mol for E.Mn ATP and E.MnADP, respectively. The relaxation rates of both complexes show strong frequency dependence, indicating that these rates are not exchange limited. Analysis of the data yields Mn(II)-2C distances of 10.0 +/- 0.5 A for E.MnATP and 8.6 +/- 0.5 A for E.MnADP. These data were interpreted, along with previously published information, on the location of the cation with respect to the phosphate chain [Jarori, G. K., Ray, B.D., & Nageswara Rao, B. D. (1985) Biochemistry 24, 3487-3494], and on the adenosine conformation [Murali, N., Jarori, G. K., & Nageswara Rao, B. D. (1993) Biochemistry 32, 12941-12948] in these complexes. The Mn(II)-2C distances depend on the orientation of the phosphate chain relative to the adenosine moiety. Conformational searches were performed by varying the two torsion angles, phi 1 (C4'-C5'-O5'-P alpha), and phi 2 (C5'-O5'-P alpha-O alpha beta), along with CHARMm energy computations, in order to determine acceptable conformations compatible with the distances determined. The significant difference in the Mn(II)-2C distances in E.MnATP and E.MnADP is indicative of the structural alterations occurring at the active site as the enzyme turns over.

Adenosine Diphosphate↗

PubMed1996

Presence of a copper(I)-thiolate regulatory domain in the copper-activated transcription factor Amt1.

The Amt1 transcription factor from Candida glabrata is activated by the formation of a tetracopper-thiolate cluster. Recombinant Amt1 (residues 1-110) is isolated as a Cu,ZnAmt1 complex. Previous mapping studies [Farrell et al. (1996) Biochemistry 35, 1571-1580] revealed that the Zn(II) site is enfolded by an independent, N-terminal domain consisting of residues 1-40. One prediction from the mapping study is that the tetracopper cluster is enfolded by residues 41-110. A truncated Amt1 peptide consisting of residues 37-110 was expressed and isolated as a CuAmt1 complex with 4 mol equiv of Cu(I) bound. The bound Cu(I) ions in the truncated Amt1 complex were spectroscopically similar to Cu(I) ions bound in the 110-mer Amt1 molecule in the energies and intensities of the ultraviolet S-->Cu charge transfer transitions and luminescence. Copper K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) of the truncated CuAmt1 complex revealed the same 2.26 A mean Cu-S bond distance as in the Cu,ZnAmt1 complex. A diagnostic feature of the polycopper-thiolate cluster in Cu,-ZnAmtl1 is the short 2.7 A Cu-Cu distance determined by Cu K-edge EXAFS. The truncated CuAmt1 complex had the same short 2.7 A Cu-Cu distance. The truncated CuAmt1 complex bound DNA specifically and with high affinity consistent with residues 41-110 being an independent domain stabilized by the tetracopper cluster. Thus, Amt1 consists of three independent and contiguous domains, an N-terminal Zn module (residues 1-40), an adjacent Cu regulatory domain (residues 41-110), and a C-terminal transcriptional activation domain. Cu(I) activation of Amt1 appears to consist of conversion of the 70-residue Cu regulatory domain from an inactive conformer to a structure containing the tetracopper cluster.

Base Sequence↗

PubMed1997

Phosphorylation-induced distance change in a cardiac muscle troponin I mutant.

Phosphorylation of two adjacent serine residues in the unique N-terminal extension of cardiac muscle troponin I (cTnI) is known to decrease the Ca2+-sensitivity of cardiac myofilaments. To probe the structural significance of the N-terminal extension, we have constructed two cTnI mutants each containing a single cysteine: (1) a full-length cTnI mutant (S5C/C81I/C98S) and (2) a truncated cTnI mutant (S9C/C50I/C67S) in which the N-terminal 32 amino acid residues were deleted. We determined the apparent binding constants for the complex formation between IAANS-labeled cardiac troponin C (cTnC) and the two cTnI mutants. The affinities of the cTnC for the truncated cTnI mutant were: (1) 1.5 x 10(6) M(-1) in EGTA, (2) 28.9 x 10(6) M(-1) in Mg2+, and (3) 87.5 x 10(6) M(-1) in Mg2+ + Ca2+. These binding constants were approximately 1.4-fold smaller than the corresponding values obtained with the full-length cTnI mutant, suggesting a very small contribution of the N-terminal extension to the binding of cTnI to cTnC. Cys-5 in the full-length cTnI mutant was labeled with IAANS, and the distribution of the separation between this site and Trp-192 was determined by analysis of the efficiency of fluorescence resonance energy transfer from Trp-192 to IAANS. The following mean distances were obtained with the unphosphorylated full-length mutant: 44.4 A (cTnI alone), 48.3 A (cTnI + cTnC), 46.3 A (cTnI + cTnC in Mg2+), and 51.6 A (cTnI + cTnC in Mg2+ + Ca2+). The corresponding values of the mean distance determined with the phosphorylated full-length cTnI mutant were 35.8, 36.6, 34.8, and 37.3 A. The phosphorylation of cTnI reduced the half-width of the distribution from 9.5 to 3.7 A. Similar but less pronounced decreases of the half-widths were also observed with the phosphorylated cTnI complexed with cTnC in different ionic conditions. Thus, phosphorylation of cTnI resulted in a decrease of 9-12 A in the mean distance between the sites located at the N- and C-terminal portion of cTnI. Our results indicate that phosphorylation elicits a change in the conformation of cTnI which underlies the basis of the phosphorylation-induced modulation of cTnI activity.

Animals↗

PubMed1997

Solution structure of a DNA decamer containing the antiviral drug ganciclovir: combined use of NMR, restrained molecular dynamics, and full relaxation matrix refinement.

The nucleoside analog 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (ganciclovir, DHPG) is an antiviral drug that is used in the treatment of a variety of herpes viruses in immunocompromised patients and in a gene therapy protocol that has shown promising activity for the treatment of cancer. To probe the structural effects of ganciclovir when incorporated into DNA, we determined and compared the solution structure of a modified ganciclovir-containing decamer duplex [d(CTG)(ganciclovir)d(ATCCAG)]2 and a control duplex d[(CTGGATCCAG)]2 using nuclear magnetic resonance techniques. 1H and 31P resonances in both duplexes were assigned using a combination of 2-D 1H and 31P NMR experiments. Proton-proton distances determined from NOESY data and dihedral angles determined from DQF-COSY data were used in restrained molecular dynamics simulations starting from canonical A- and B-form DNA models. Both the control and ganciclovir sets of simulations converged to B-type structures. These structures were subjected to full relaxation matrix refinement to produce final structures that were in excellent agreement with the observed NOE intensities. Examination of the final ganciclovir-containing structures reveals that the base of the ganciclovir residue is hydrogen bonded to its complementary dC and is stacked in the helix; in fact, the base of ganciclovir exhibits increased stacking with the 5' base relative to the control. Interestingly, some of the most significant distortions in the structures occur 3' to the lesion site, including a noticeable kink in the sugar-phosphate backbone at this position. Further examination reveals that the backbone conformation, sugar pucker, and glycosidic torsion angle of the residue 3' to the lesion site all indicate an A-type conformation at this position. A possible correlation of these structural findings with results obtained from earlier biochemical studies will be discussed.

Antiviral Agents↗

PubMed1998

The conformation of NADH bound to inosine 5'-monophosphate dehydrogenase determined by transferred nuclear Overhauser effect spectroscopy.

Inosine 5'-monophosphate dehydrogenase (IMPDH) catalyzes the oxidation of inosine 5-monophosphate (IMP) to xanthosine 5'-monophosphate (XMP). The reaction proceeds with concomitant conversion of NAD+ to NADH and is the rate-limiting step in the de novo biosynthesis of guanosine nucleotides. IMPDH is a target for numerous chemotherapeutic agents. The conformations of enzyme-bound substrates, enzyme-bound products and enzyme-bound ligands in general, are of interest for the understanding of the catalytic mechanism of the enzyme and the design of new inhibitors. Although several of the chemotherapeutic inhibitors of IMPDH are NAD+ or NADH analogues, no structural data for IMPDH-bound NAD+ (or NADH) are available. In the present work, we have used transferred nuclear Overhauser effect spectroscopy (TRNOESY) to determine the conformation of NADH bound to the active site of human type II IMPDH (IMPDH-h2). The inter-proton distances determined from TRNOESY data indicate that NADH binds to the enzyme active site in an overall extended conformation. The adenosine moiety and the nicotinamide riboside moiety are both in the anti conformation about the glycosidic bond, and both ribose rings are in approximately C4'-exo conformations. The nicotinamide amide group was found to be in a cis conformation. The anti conformation of the nicotinamide riboside moiety is in accord with the preferred conformations of several potent and selective dinucleotide inhibitors and is consistent with that implied by the stereospecificity of hydride transfer in the enzymatic reaction. The implications of this conformation for the catalytic mechanism of IMPDH-h2 are discussed.

Adenosine↗

PubMed1998

Hybridization of peptide nucleic acid.

The thermodynamics of hybridization and the conformations of decameric mixed purine-pyrimidine sequence PNA/PNA, PNA/DNA, and DNA/DNA duplexes have been studied using fluorescence energy transfer (FET), absorption hypochromicity (ABS), isothermal titration calorimetry (ITC), and circular dichroism (CD) techniques. The interchromophoric distances determined in the FET experiments on fluorescein- and rhodamine-labeled duplexes indicate that the solution structures of the duplexes are extended helices in agreement with available NMR (PNA/DNA) and crystal X-ray data (PNA/PNA). The melting thermodynamics of the duplexes was studied with both FET and ABS. The thermodynamic parameters obtained with ABS are in good agreement with the parameters from calorimetric measurements while FET detection of duplex melting gives in most cases more favorable free energies of hybridization. This discrepancy between FET and ABS detection is ascribed to the conjugated dyes which affect the stability of the duplexes substantially. Especially, the dianionic fluorescein attached via a flexible linker either to PNA or to DNA seems to be involved in an attractive interaction with the opposite dicationic lysine when hybridized to a PNA strand. This interaction leads to an increased thermal stability as manifested as a 3-4 degreesC increase of the melting temperature. For the PNA/DNA duplex where fluorescein is attached to the PNA strand, a large destabilization (DeltaTm = -12 degreesC) occurs relative to the unlabeled duplex, probably originating from electrostatic repulsion between the fluorescein and the negatively charged DNA backbone. In the case of the PNA/PNA duplex, the sense of helicity of the duplex is reversed upon conjugation of fluorescein via a flexible linker arm, but not when the fluorescein is attached without a linker to the PNA.

Circular Dichroism↗

PubMed1998

Electric fish measure distance in the dark.

Distance determination in animals can be achieved by visual or non-visual cues. Weakly electric fish use active electrolocation for orientation in the dark. By perceiving self-produced electric signals with epidermal electroreceptors, fish can detect, locate and analyse nearby objects. Distance discrimination, however, was thought to be hardly possible because it was assumed that confusing ambiguity could arise with objects of unknown sizes and materials. Here we show that during electrolocation electric fish can measure the distance of most objects accurately, independently of size, shape and material. Measurements of the 'electric image' projected onto the skin surface during electrolocation revealed only one parameter combination that was unambiguously related to object distance: the ratio between maximal image slope and maximal image amplitude. However, slope-to-amplitude ratios for spheres were always smaller than those for other objects. As predicted, these objects were erroneously judged by the fish to be further away than all other objects at an identical distance. Our results suggest a novel mechanism for depth perception that can be achieved with a single, stationary two-dimensional array of detectors.

Animals↗

PubMed1991

Protein solution structure determination using distances from two-dimensional nuclear Overhauser effect experiments: effect of approximations on the accuracy of derived structures.

Solution structures for many proteins have been determined to date utilizing interproton distance constraints estimated from two-dimensional nuclear Overhauser effect (2D NOE) spectra. Although the simple isolated spin pair approximation (ISPA) generally used can result in systematic errors in distances, the large number of constraints enables protein structure to be defined with reasonably high resolution. Effects of these systematic errors on the resulting protein structure are examined. Iterative relaxation matrix calculations, which account for dipolar interactions between all protons in a molecule, can accurately determine internuclear distances with little or no a priori knowledge of the molecular structure. The value of this additional complexity is also addressed. To assess these distance determination methods, hypothetical "experimental" data, including random noise and peak overlap, are calculated for an arbitrary "true" protein structure. Three methods of obtaining distance constraints from 2D NOE peak intensities are examined: one entails a conservative use of ISPA, one assumes the ISPA to be fairly accurate, and one utilizes an iterative relaxation matrix method called MARDIGRAS (matrix analysis of relaxation for discerning the geometry of an aqueous structure), developed in this laboratory. A distance geometry algorithm was used to generate a family of structures for each distance set. The quality of the average structure from each family was good. The root-mean-square deviation of that average structure from the true structure was improved about 2-5% using the more restrictive rather than the more conservative ISPA approach. Use of MARDIGRAS in a conservative fashion--i.e., with a poor initial model--resulted in improvement in the root-mean-square deviation by 8-15%. With a better initial model, MARDIGRAS obtained even more accurate distances. MARDIGRAS also permits analysis of 2D NOE data at longer mixing times, yielding additional distances. Use of more restrictive ISPA distances did, however, result in a few systematically incorrect structural features in local regions of the protein, producing distortions of 2-3 A. Comparison between experimental data and spectra calculated for the structures correlates with root-mean-square deviation, offering a method of structure evaluation. An R factor for evaluating fit between experimental and calculated 2D NOE intensities is proposed.

Magnetic Resonance Spectroscopy↗

PubMedDate not supplied

The geographic clustering of body size of Chinese children aged 7 years.

We studied the morphological differences and similarities among Chinese Han children aged 7 years by using PCA-Q mode cluster analysis. The data were drawn from 17,119 boys and 17,084 girls who came from 28 provinces and participated in the 1985 National Survey on Students Constitution and Health. The children were divided into urban and rural subgroups in each province. First, the values of six measures of body size (stature, sitting height, body weight, chest girth, biacromial diameter and biiliocristal diameter) were normalized into principal component scores; and then clustering was performed among subgroups according to the distances determined by the component scores. The results show significant variations in children's body size exist not only between north and south China, but also between developed and under-developed districts and between urban and rural areas. The geographic and socio-economic factors causing these variations were investigated. The practical use of PCA-Q cluster analysis and its merits in studying Chinese children's growth variations are discussed.

Anthropometry↗

PubMed1987

An abasic site in DNA. Solution conformation determined by proton NMR and molecular mechanics calculations.

We have determined the three-dimensional structure of a non-selfcomplementary nonanucleotide duplex which contains an abasic (apyrimidinic) site in the centre, i.e. a deoxyribose residue opposite an adenosine. The majority of the base and sugar proton resonances were assigned by NOESY, COSY and 2DQF spectra in D2O and H2O. We have measured the initial slope of buildup of NOEs in NOESY spectra at very short mixing times (25 to 50 ms), and from these were able to establish interproton distances for the central part of the duplex. We propose a different strategy for proton-proton distance determinations which takes into account the observed variations in correlation times for particular proton-proton vectors. A set of 31 measured interproton distances was incorporated into the refinement of the oligonucleotide structure by molecular mechanics calculations. Two structures were obtained which retain all aspects of a classical B DNA in which the unpaired adenine and the abasic deoxyribose lie inside the helix. We observe that the non-hydrogen bonded adenine is held well in the helix, the Tm of this base being the same as that of the A.T base pairs in the same duplex.

Algorithms↗

PubMed1988

DNA divergence in and around the alcohol dehydrogenase locus in five closely related species of Hawaiian Drosophila.

The alcohol dehydrogenase (Adh) region from five planitibia subgroup species of Hawaiian picture-wing Drosophila has been cloned. A total of 15 kb of DNA in and around the Adh gene has been compared among the five species. Genetic distances were calculated to determine evolutionary relationships. These distances agree with previous distances determined by protein polymorphism and DNA hybridization techniques and can be interpreted in terms of specific island colonization and speciation (founder) events over the past 5 Myr. Examination of the restriction maps of the cloned Adh region from the five species shows many instances of small deletions, insertion of a transposable element in D. heteroneura, and the existence of a highly variable region on the 3' side of the Adh gene. Clustering relationships and rates of DNA change are calculated and compared with the relationship found for other species of Drosophila.

Alcohol Dehydrogenase↗

PubMed1996

Effects of the sulphydryl donor N-acetyl-L-cysteine on nerve conduction, perfusion, maturation and regeneration following freeze damage in diabetic rats.

Peripheral nerve conduction velocity deficits in diabetic rats depend on decreased nerve perfusion, which may be related to increased free radical activity and impaired endogenous protection by the glutathione redox cycle. We studied the effect of treatment with the glutathione precursor N-acetyl-L-cysteine on nerve conduction, blood flow, maturation and regeneration. Two months of diabetes in mature rats caused 20% and 48% deficits in sciatic motor conduction velocity and endoneurial blood flow, respectively, which were largely corrected by N-acetyl-L-cysteine treatment during the second month. In young nondiabetic rats, sciatic motor conduction velocity increased by 31% over 6 weeks. Diabetes halved the conduction velocity maturation rate, however N-acetyl-L-cysteine treatment allowed a normal pattern of development. After 1 month of treated or untreated diabetes, the sciatic nerve was lesioned by a liquid nitrogen-cooled probe. Myelinated fibre regeneration distance, determined electrophysiologically, was reduced by 12.2% with diabetes; this was prevented by N-acetyl-L-cysteine treatment. Thus, the data stress the importance of free radical-mediated changes in the aetiology of experimental diabetic neuropathy.

Acetylcysteine↗

PubMed1981

Synthesis of 8-L-tryptophan-oxytocin and determination of one of its conformational parameters.

The hormone analog 8-L-tryptophan-oxytocin was synthesized in solution by stepwise chain lengthening from the C-terminal residue. Active esters of 9-fluorenylmethyloxycarbonyl (Fmoc)-amino acids were used for the incorporation of individual residues and thereby exposure to the tryptophan-containing intermediates both to acid conditions and to alkylation could be avoided. In a parallel experiment the parent compound, oxytocin, was prepared similarly. The final products were purified by countercurrent distribution. The presence of tyrosine (donor) and tryptophan (acceptor) in the chain was used for the measurement of the average intramolecular Tyr2-Trp8 distance by evaluation of intramolecular resonance energy transfer between their fluorescent side chains. Since the 8-L-tryptophan analog has high affinity for oxytocin receptors, it is reasonable to assume that its conformation is similar to that of the parent molecule and that in the latter the leucine-tyrosine distance is of about the same length. The distance of 13.5 Ao between the side chains of tyrosine and tryptophan measured in aqueous solution is compatible with the Tyr2-Leu8 distance determined with molecular models built according to the proposals of Walter for the biologically active conformation of oxytocin.

Amino Acid Sequence↗

PubMed1990

Mapping of glucose and glucose-6-phosphate binding sites on bovine brain hexokinase. A 1H- and 31P-NMR investigation.

Inhibition of bovine brain hexokinase by its product, glucose 6-phosphate, is considered to be a major regulatory step in controlling the glycolytic flux in the brain. Investigations on the molecular basis of this regulation, i.e. allosteric or product inhibition, have led to various proposals. Here, we attempt to resolve this issue by ascertaining the location of the binding sites for glucose and glucose 6-phosphate on the enzyme with respect to a divalent-cation-binding site characterized previously [Jarori, G. K., Kasturi, S. R. & Kenkare, U. W. (1981) Arch. Biochem. Biophys. 211, 258-268]. The paramagnetic effect of enzyme-bound Mn(II) on the spin-lattice relaxation rates (T-1(1] of ligand nuclei (1H and 31P) in E.Mn(II).Glc and E.Mn(II).Glc6P complexes have been measured. The paramagnetic effect of Mn(II) on the proton relaxation rates of C1-H alpha, C1-H beta and C2-H beta of glucose in the E.Mn(II).Glc complex was measured at 270 MHz and 500 MHz. The temperature dependence of these rates was also studied in the range of 5-30 degrees C at 500 MHz. The ligand nuclear relaxation rates in E.Mn(II).Glc are field-dependent and the Arrhenius plot yields an activation energy (delta E) of 16.7-20.9 kJ/mol. Similar measurements have also been carried out on C1-H alpha, C1-H beta and C6-31P at 270 MHz (1H) and 202.5 MHz (31P) for the E.Mn(II).Glc6P complex. The temperature dependence of 31P relaxation rates in this complex was measured in the range 5-30 degrees C, which yielded delta E = 9.2 kJ/mol. The electron-nuclear dipolar correlation time (tau c), determined from the field-dependent measurements of proton relaxation rates in the E.Mn(II).Glc complex, is 0.22-1.27 ns. The distances determined between Mn(II) and C1-H of glucose and glucose 6-phosphate are approximately 1.1 nm and approximately 0.8 nm, respectively. These data, considered together with our recent results [Mehta, A., Jarori, G. K. & Kenkare, U. W. (1988) J. Biol. Chem. 263, 15492-15498], suggest that glucose and glucose 6-phosphate may bind to very nearly the same region of the enzyme. The structure of the binary Glc6P.Mn(II) complex has also been determined. The phosphoryl group of the sugar phosphate forms a first co-ordination complex with the cation. However, on the enzyme, the phosphoryl group is located at a distance of approximately 0.5-0.6 nm from the cation.

Animals↗

PubMed1988

Molecular phylogeny of the animal kingdom.

A rapid sequencing method for ribosomal RNA was applied to the resolution of evolutionary relationships among Metazoa. Representatives of 22 classes in 10 animal phyla were used to infer phylogenetic relationships, based on evolutionary distances determined from pairwise comparisons of the 18S ribosomal RNA sequences. The classical Eumetazoa are divided into two groups. Cnidarians arose from a protist ancestry different from the second group, the Bilateria. Within the Bilateria, an early split gave rise to Platyhelminthes (flatworms) and the coelomate lineage. Coelomates are thus monophyletic, and they radiated rapidly into four groups: chordates, echinoderms, arthropods, and eucoelomate protostomes.

Animals↗

PubMed1966

Fine-structure mapping by transformation in the tryptophan region of Bacillus subtilis.

Carlton, Bruce C. (Yale University, New Haven, Conn.). Fine-structure mapping by transformation in the tryptophan region of Bacillus subtilis. J. Bacteriol. 91:1795-1803. 1966.-The arrangements of eight mutational sites within a segment of the tryptophan cluster of Bacillus subtilis have been determined by three-point reciprocal crosses with a mutation in the same gene cluster used as an outside marker. Estimates of distances between sites were made by two-point crosses and normalization to recombination values for an unlinked marker to correct for physiological variabilities between recipient strains. In general, the additivities of map distances determined by this procedure were reasonable, although some discrepancies were noted in reciprocal crosses between widely separated sites within the gene region examined. No definitive polarity effect on recombination was evident, and it appears that the variations observed in reciprocal crosses may be an effect of the probability of recovery of crossovers between exogenotic and endogenotic segments. It is concluded that fine-structure mapping is feasible for the transformation system in this organism and that a high degree of resolution can be attained.

Bacillus subtilis↗

PubMed1999

Active electrolocation of objects in weakly electric fish

Weakly electric fish produce electric signals (electric organ discharges, EODs) with a specialised electric organ creating an electric field around their body. Objects within this field alter the EOD-induced current at epidermal electroreceptor organs, which are distributed over almost the entire body surface. The detection, localisation and analysis of objects performed by monitoring self-produced electric signals is called active electrolocation. Electric fish employ active electrolocation to detect objects that are less than 12 cm away and have electric properties that are different from those of the surrounding water. Within this range, the mormyrid Gnathonemus petersii can also perceive the distance of objects. Depth perception is independent of object parameters such as size, shape and material. The mechanism for distance determination through electrolocation involves calculating the ratio between two parameters of the electric image that the object projects onto the fish's skin. Electric fish can not only locate objects but can also analyse their electrical properties. Fish are informed about object impedance by measuring local amplitude changes at their receptor organs evoked by an object. In addition, all electric fish studied so far can independently determine the capacitative and resistive components of objects that possess complex impedances. This ability allows the fish to discriminate between living and non-living matter, because capacitance is a property of living organisms. African mormyrids and South American gymnotiforms use different mechanisms for capacitance detection. Mormyrids detect capacitance-evoked EOD waveform distortions, whereas gymnotiforms perform time measurements. Gymnotiforms measure the temporal phase shift of their EODs induced at body parts close to the object relative to unaffected body parts further away.

Journal Article↗

PubMed1981

Estimation of inter-electrode distance for body surface mapping: application of Fourier analysis to potential distribution due to the epicardial breakthrough.

For the purpose of determining an appropriate distance of lead points for constructing body surface maps, Fourier analysis was performed on potential distribution reflecting the epicardial breakthrough, and inter-electrode distance necessary for sampling of harmonics contributing to the body surface potential distribution was determined by application of sampling theorem. Potential distribution was simultaneously recorded with an interval of 4 mm for 250 msec along the vertical (head to foot) and horizontal (right to left) line crossing a second-minimum appearing on the chest surface of a healthy adult, and the data obtained from 9.6 cm along the respective lines underwent Fourier transform. Relative contribution of the second harmonics to the original wave forms increased with time lapse after QRS initiation, in accordance with reductions of the first harmonics component, and attained the maximum (32.5% of total power spectrum without d-c component) at the instant of occurrence of the second-minimum. A similar tendency was observed among higher harmonics, but their contribution was comparatively low (within 10%). Inter-electrode distance determined by sampling theorem was 4.8 cm for the first harmonics and 2.4 cm for the second harmonics. In conclusion it is proposed that placement of electrodes with an inter-electrode distance of 2.4 cm is necessary for acquiring clinically important data on the epicardial breakthrough.

Electrocardiography↗