Showing papers in "Quarterly Reviews of Biophysics in 1991"

Physical properties of the fluid lipid-bilayer component of cell membranes: a perspective.

Abstract: The motivation for this review arises from the conviction that, as a result of the mass of experimental data and observations collected in recent years, the study of the physical properties of membranes is now entering a new stage of development. More and more, experiments are being designed to answer specific, detailed questions about membranes which will lead to a quantitative understanding of the way in which the physical properties of membranes are related to and influence their biological function.

Bacteriorhodopsin: a biological material for information processing

Abstract: Technology which makes use of biological materials has advanced dramatically in the last few decades. Production of specific biochemicals by selected microbial strains, the use of enzymes for stereospecific biosynthesis of materials and gene technological production of biologically important macromolecules are a few examples of these developments.

Protein dynamics: comparison of simulations with inelastic neutron scattering experiments.

Abstract: To deepen our understanding of the principles determining the folding and functioning of globular proteins the determination of their three-dimensional structures must be supplemented with the characterization of their internal motions. Although dynamical events in proteins occur on time-scale ranging from femtoseconds to at least seconds, the physical properties of globular proteins are such that picosecond (ps) time-scale motions make a particularly important contribution to the internal fluctuations of the atoms from their mean positions.

RNA structure and NMR spectroscopy.

Abstract: RNA molecules perform a wide variety of biological functions, from enzymic activity to storage and propagation of genetic information.

Ca2+ and activation mechanisms in skeletal muscle.

Abstract: It has been known for a number of years that calcium ions play a crucial role in excitation-contraction (e-c) coupling (Sandow, 1952). The majority of the calcium required for this process is derived, at least in vertebrate striated muscle fibres, from discrete intracellular stores located at sites within the cell: the terminal cysternae (tc)/junctional SR of the sarcoplasmic reticulum (SR) (Fig. 1 a). These storage sites not only form a compartment that is distinct from the sarcoplasm of the fibre, but they are also closely associated with the contractile elements, the myofibrils. The SR release sites are activated following the spread of electrical activity (Huxley and Taylor, 1958) along the transverse (T) tubular system (Eisenberg and Gage, 1967; Adrian et al. 1969a, b; Peachey, 1973) from the surface membrane (Bm).

Time-resolved capacitance measurements: monitoring exocytosis in single cells.

Abstract: Many cells release preformed material contained in secretory granules by exocytosis. Exocytosis is a specialized means of secretion in which the granules fuse with the plasma membrane and thereby discharge their contents through the fusion pores. This mechanism mediates, for example, the formation of the fertilization envelope in eggs, the release of neurotransmitters and neuropeptides by neurons, the release of a variety of enzymes and mediators by mast cells and granulocytes or the secretion of hormones by endocrine cells. Classical methods for investigating exocytosis usually measure release of secreted material.

Microscopic behaviour of DNA during electrophoresis: electrophoretic orientation.

Abstract: The study of the behaviour of DNA when subjected to electric fields poses several intriguing problems of fundamental physico-chemical importance. Electric field (Kerr effect) orientation of DNA in free solution as well as migration of DNA in gel electrophoresis are two well-established, but so far rather separate, research fields. Whereas the first one has been generally concerned with basic structural and dynamical properties of DNA (Charney, 1988), the second is closely related to techniques of molecular biology (for a review on DNA electrophoresis, see stellwagen 1987).

Biophysical processes in invertebrate photoreceptors: recent progress and a critical overview based on Limulus photoreceptors.

Abstract: Limulus ventral nerve photoreceptor, a classical preparation for the study the phototransduction in invertebrate eyes, seems to have a very complex mechanism to transform light energy into a physiological signal. Although the main function of the photoreceptor is to change the membrane conductance according to the illumination, the cell has voltage-activated conductances as well. The voltage-gated conductances are matched to the light-activated ones in the sense that they make the function of the cell more efficient. The complex mechanism of phototransduction and the presence of four different voltage-gated conductance in Limulus ventral nerve photoreceptors indicate that these cells are far less differentiated than the photoreceptor cells of vertebrates. Indications accumulated in recent years support the view that the ventral photoreceptor of Limulus has different light-activated macroscopic current components, ion channels and terminal transmitters. After conclusions from macroscopic current measurements (Payne, 1986; Payne et al. 1986 a, b), direct evidence was presented by single-channel (Nagy & Stieve, 1990 a, b; Nagy, 1990 a, b) and macroscopic current measurements (Deckert et al. 1991 a, b) for three different light-activated conductances. It has been shown that two of these conductances are stimulated by two different excitation mechanisms. The two mechanisms, having different kinetics, release probably two different transmitters. One of them might be the cGMP (Johnson et al. 1986), the other one the calcium ion (Payne et al. 1986 a, b). However, the biochemical processes which link the rhodopsin molecules and the ion channels are not known. The unknown chemical details of the phototransduction result in a delay for the mathematical description of the biophysical mechanisms. More biochemical details are known about the adaptation mechanism. It was found that inositol 1,4,5-trisphosphate is a messenger for the release of calcium ions from the intracellular stores and that calcium ions are the messengers for adaptation (Payne et al. 1986 b; Payne & Fein, 1987). Concerning the mechanism of calcium release, it was revealed that a negative feedback acts on the enzyme cascade to regulate the internal calcium level and to protect the stores against complete emptying (Payne et al. 1988, 1990). Calcium ions also play an important role in the excitation mechanism. (a) In [Ca2+]i-depleted cells the light-induced current was increased after intracellular Ca2+ injection, suggesting that calcium is necessary for the transduction mechanism (Bolsover & Brown, 1985).(ABSTRACT TRUNCATED AT 400 WORDS)

The application of the molecular replacement method to the de novo determination of protein structure.

Abstract: The determination of a novel protein structure by X-ray diffraction is seldom straightforward. Three hurdles present themselves (i) the protein must be purified in sufficient quantity to allow crystallization trials, (ii) crystals must be grown to adequate size and must diffract to a resolution that will allow atomic detail to be revealed, and (iii) phases must be determined for the diffracted X-ray beams in order that an initial electron-density map may be calculated.