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Biomedical subjects

J Kistler

Publications and source records attributed to J Kistler.

69 records · Page 4Linked to original sources
PubMed1981

Crystalline arrays of membrane-bound acetylcholine receptor.

Electron micrographs of tubular structures with a crystalline arrangement of membrane-bound acetylcholine receptor oligomers have been analyzed by digital image reconstruction. The receptor molecules are oriented synaptic side out, and in projection they appear to be asymmetric and have a defined orientation. All four subunits are contained in the oligomers as demonstrated by immunoelectron microscopy; these structures therefore appear to be suitable for subunit localization in the oligomer.

Animals↗
PubMed1977

New method for localizing proteins in periodic structures: Fab fragment labeling combined with image processing of electron micrographs.

Fab fragments prepared from antisera directed against purified bacteriophage T4 structural proteins and head-related structures were used to label proteins on the surface of T-even giant phage capsids. Optically filtered electron micrographs of the Fab-labeled capsids reveal both the location of specific proteins within the capsomeres and differing conformational states of the protein subunits. We describe parameters affecting the utility of this technique for the study of molecular organization and protein conformation in periodic biological structures.

Antibodies, Viral↗
PubMed1977

Ultrastructure of a periodic protein layer in the outer membrane of Escherichia coli.

Matrix protein (36,500 daltons), one of the major polypeptides of the Escherichia coli cell envelope, is arranged in a periodic monolayer which covers the outer surface of the peptidoglycan. Although its association with the peptidoglycan layer is probably tight, the periodic structure of the peptidoglycan. Although its association with the peptidoglycan later is probably tight, the periodic structure is maintained in the absence of peptidoglycan, and is therefore based on strong protein-protein interactions. A detailed analysis of the ultrastructure of the matrix protein array by electron microscopy and image processing of specimens prepared by negative staining or by freeze-drying and shadowing shows that the molecules are arranged according to three fold symmetry on a hexagonal lattice whose repeat is 7.7 nm. The most pronounced feature of the unit cell, which probably contains three molecules of matrix protein, is a triplet of indentations, each approx. 2 nm in diameter, with a center-to-center spacing of 3nm. They are readily penetrated by stain and may represent channels which span the protein monolayer.

Bacterial Proteins↗
PubMed1976

Comparison of the structural and chemical composition of giant T-even phage heads.

A study has been made of the structure of the capsids of T4D giant phage produced from mutants in gene 23 and temperature-sensitive mutants in gene 24, and T4D and T2L giant phage formed by the addition of L-canavanine followed by an Larginine chase in the growth medium. All the giant phage capsids have been shown to be built according to the same geometrical architecture. This consists of a near-hexagonal surface net, lattice constant 129.5 A, folded into a left-handed T = 13 prolate icosahedron elongated along one of its fivefold symmetry axes. Their only apparent difference from wild-type T-even phage capsids is their abnormally elongated tubular part. A comparison of the capsomere morphologies and protein compositions of the giant phage capsids showed that all T4D giants are identical but differ from T2L: The T4D capsomere has a complex (6 + 6 + 1)-type morphology, whereas the T2L has a simple 6-type. T2L phage, however, lack two capsid proteins, "soc" and "hoc", present in T4D. The difference in capsomere morphology can therefore be related to the difference in the protein compositions of these two phage. Possible differences between the initiation and means of length regulation of giant phage heads and the aberrant polyheads are discussed.

Capsid↗
PubMedDate not supplied

Two distinct levels of gap junction assembly in vitro.

The in vitro assembly of crystalline gap junctions from detergent-solubilized sheep lens fiber cell pore complexes in the presence of endogenous lipid is a two-step process. "Mini"-gap junctions containing about 10 pore complexes assembled within 12 hr of dialysis. The removal of detergent appeared to be the sole factor required to reach this level of assembly. Further growth to micrometer-sized crystalline gap junctions required cleaved connexin, MgCl2, elevated dialysis temperature, and dialysis for 3-5 days. Molecular interactions between adjacent pore structures laterally in the membrane are vital for the second phase of assembly but appear to be of minor importance for the formation of mini-gap junctions. Parallels exist between structural aspects of gap junction assembly in vitro and the 2-D crystallization of membrane proteins in general.

Animals↗
PubMedDate not supplied

Assembly of 2-D membrane protein crystals: dynamics, crystal order, and fidelity of structure analysis by electron microscopy.

Membrane protein reconstitution into two-dimensional (2-D) ordered arrays is described. The assembly of 2-D crystals may be modeled as a two-step process: the membrane protein is first integrated in the lipid bilayer and then crystallized by removal of excess detergent or lipid and/or by precipitating agents. Lipid-detergent, protein-detergent, and lipid-protein interactions are critical during the first step, while lipid-protein and protein-protein interactions dominate events in the second step. The evidence supporting this model results from quasielastic light scattering analyses and electron microscopy of different lipid-detergent systems and reconstitution experiments with Escherichia coli porin OmpF, Phormidium laminosum photosystem I reaction centers, and integral membrane proteins of mammalian lens fiber cells.

Animals↗
PubMedDate not supplied

The AAMI standard test load for electrical risk current measurements.

The AAMI standard test load prescribed in AAMI's American National Standard, Safe Current Limits for Electromedical Apparatus, addresses the need to accurately measure electrical risk currents associated with the use of electromedical patient care equipment. Its purpose is to simulate a good electrical contact to the body and to roughly approximate the body's physiological response to electrical current flow as a function of frequency. Although the AAMI test load meets these needs well for most measurement situations, it may overstate the risk current arising from low-impedance sources when higher frequencies (greater than 1 kHz) are present. This problem of source impedance emphasizes the need for standards to express requirements in terms of performance rather than to require that specific test methods be used. Specific test methods may be appropriate if they adequately cover the requirements of the measurement or if any limitations they have are clearly understood by everyone. The present AAMI test load can remain an effective measurement tool, provided users understand its limitations.

Electric Conductivity↗