Biomedical subjects

E M Goodman

Publications and source records attributed to E M Goodman.

At least 19 recordsLinked to original sources

PubMed1991

Periodicity of amide proton exchange rates in a coiled-coil leucine zipper peptide.

The two-stranded coiled-coil motif, which includes leucine zippers, is a simple protein structure that is well suited for studies of helix-helix interactions. The interaction between helices in a coiled coil involves packing of "knobs" into "holes", as predicted by Crick in 1953 and confirmed recently by X-ray crystallography for the GCN4 leucine zipper [O'Shea, E.K., Klemm, J.D., Kim, P.S., & Alber, T. (1991) Science 254, 539]. A striking periodicity, extending over six helical turns, is observed in the rates of hydrogen-deuterium exchange for amide protons in a peptide corresponding to the leucine zipper of GCN4. Protons at the hydrophobic interface show the most protection from exchange. The NMR chemical shifts of amide protons in the helices also show a pronounced periodicity which predicts a short H-bond followed by a long H-bond every seven residues. This variation was anticipated in 1953 by Pauling and is sufficient to give rise to a local left-handed superhelical twist characteristic of coiled coils. The amide protons that lie at the base of the "hole" in the "knobs-into-holes" packing show slow amide proton exchange rates and are predicted to have short H-bond lengths. These results suggest that tertiary interactions can lead to highly localized, but substantial, differences in stability and dynamics within a secondary structure element and emphasize the dominant nature of packing interactions in determining protein structure.

Amides↗

PubMed1991

An increase in the negative surface charge of U937 cells exposed to a pulsed magnetic field.

Pulsed magnetic fields have been used to enhance healing of bone fractures and purportedly of lesions in soft tissue. However, their mechanism of action is poorly understood. We report changes in the plasma membrane of a nonadherent mammalian cell line, U937, which was exposed to a 25-pps magnetic field for 48 hours. Aqueous polymer two-phase partition studies showed that magnetic-field-exposed cells exhibited an increased negative surface charge but membrane hydrophobicity was not significantly altered. The observed increase in membrane electronegativity of exposed cells did not reflect a significant change in growth rate.

Cell Line↗

PubMed1989

Folding of a peptide corresponding to the alpha-helix in bovine pancreatic trypsin inhibitor.

A short peptide corresponding to the alpha-helical region of BPTI shows partial folding in aqueous solution (pH 7) as judged by circular dichroism (CD). Folding is temperature and denaturant sensitive, and the peptide is monomeric. The difference CD spectrum, obtained from spectra at two temperatures, indicates that the peptide folds as an alpha-helix. Difference CD spectroscopy provides a sensitive assay for helix formation in peptides exhibiting small amounts of structure. Helix stability in this peptide shows a marked pH dependence which is consistent with stabilizing charged side-chain interactions with the helix dipole and/or salt bridge formation.

Animals↗

PubMed1988

Low frequency electric and magnetic fields have different effects on the cell surface.

There is a considerable controversy over the nature of weak electromagnetic-field effects in living organisms. Part of the controversy can be traced to a lack of understanding of whether electric or magnetic fields are involved in producing bioeffects. We find that both 60 Hz electric and magnetic fields alter the cell surface of Physarum polycephalum. Exposure to electric fields increases the negative charge on the cell surface while magnetic-field exposure decreases the hydrophobic character of the surface. These effects appear to be additive and independent of the waveform of the applied fields.

Cell Membrane↗

PubMed1986

Pulsed magnetic fields alter the cell surface.

Pulsed magnetic fields (PMFS) are routinely used in the medical community to facilitate bone repair in clinical cases of non-union or pseudarthoses [(1984) Orth. Clin. No. Am. 15, 61-87]. Although this therapeutic regimen appears to be reasonably effective, the mechanism of action between specific PMFs and the target tissue remains unknown. Adding urgency to the need to understand the mechanism are a wide number of reports that have appeared which demonstrate that PMFs similar to those in clinical use can alter many basic physiological functions. We report that a 24 h exposure to PMFs alters the cell surface of Physarum polycephalum amoebae. Further, using the technique of aqueous two-phase partitioning, we present evidence for individual magnetic and electric field, cell surface effects.

Cell Membrane↗

PubMed1986

Effects of sinusoidal 60-Hz electric and magnetic fields on ATP and oxygen levels in the slime mold, Physarum polycephalum.

We have previously reported that exposing the vegetative plasmodia stage of Physarum polycephalum to either individual or simultaneously applied electric and magnetic fields (45-75 Hz, 0.14-2.0 G, and 0.035-0.7 V/m) lengthens their mitotic cycle, depresses their rate of reversible shuttle streaming, and lowers their respiration rate. In this article we report the effects of simultaneously applied electromagnetic fields (60 Hz, 1.0 G, 1.0 V/m), electric fields only (60 Hz, 1.0 V/m), magnetic fields only (60 Hz, 1.0 G) on the haploid amoeba of Physarum exposed for 120-180 days. Statistically significant depressions (about 8-11%) in ATP levels were observed with all field conditions; however, respiration was significantly decreased only when amoebae were subjected to either combined fields or electric fields alone. Magnetic fields alone failed to induce a significant decrease in respiration.

Adenosine Triphosphate↗

PubMed1986

Differences in the surface properties of the mating types of Physarum polycephalum.

In the slime mold Physarum polycephalum, formation of a diploid plasmodium occurs when compatible haploid amoebae fuse. To study cell surface changes associated with the fusion process, a non-destructive method known as aqueous, two-phase partitioning was employed. Using a two-phase system of dextran and polyethylene glycol, we observed that the two mating types (RSD4 and MA185) have different partition coefficients and hence different surface properties. Based on their partitioning behavior, MA185 cells appear to have a more hydrophobic surface than RSD4 amoeba. The partition coefficient of both cell types decreased with time. If amoebae were maintained in culture until they encysted, differences in their surface were not detectable.

Physarum↗

PubMed1979