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A Grinvald

Publications and source records attributed to A Grinvald.

62 records · Page 4Linked to original sources
PubMed1976

The fluorescence decay of tryptophan residues in native and denatured proteins.

The fluorescence decay kinetics at different ranges of the emission spectrum is reported for 17 proteins. Out of eight proteins containing a single tryptophan residue per molecule, seven proteins display multiexponential decay kinetics, suggesting that variability in protein structure may exist for most proteins. Tryptophan residues whose fluorescence spectrum is red shifted may have lifetimes longer than 7 ns. Such long lifetimes have not been detected in any of the denatured proteins studied, indicating that in native proteins the tryptophans having a red-shifted spectrum are affected by the tertiary structure of the protein. The fluorescence decay kinetics of ten denatured proteins studied obey multiexponential decay functions. It is therefore concluded that the tryptophan residues in denatured proteins can be grouped in two classes. The first characterized by a relatively long lifetime of about 4 ns and the second has a short lifetime of about 1.5 ns. The emission spectrum of the group which is characterized by the longer lifetime is red shifted relative to the emission spectrum of the group characterized by the shorter lifetime. A comparison of the decay data with the quantum yield of the proteins raises the possibility that a subgroup of the tryptophan residues is fully quenched. It is noteworthy that despite this heterogeneity in the environment of tryptophan residues in each denatured protein, almost the same decay kinetics has been obtained for all the denatured proteins studied in spite of the vastly different primary structures. It is therefore concluded that each tryptophan residue interacts in a more-or-less random manner with other groups on the polypeptide chain, and that on the average the different tryptophan residues in denatured proteins have a similar type of environment.

Hydrogen-Ion Concentration↗
PubMed1975

Homogeneity and variability in the structure of azurin molecules studied by fluorescence decay and circular polarization.

The fluorescence decay of apoazurin derived from Pseudomonas aeruginosa is monoexponential. By this criterion the population of molecules of apoazurin is homogeneous. The emission anisotropy factor and the absorption anisotropy factor at the red edge of the absorption band assume similar values, showing that the tryptophan residue in apoazurin has the same asymmetric environment both in the ground and excited states. This finding suggests tight packing of the protein at the tryptophan environment. Native azurin does not decay monoexponentially. Moreover, comparison between the quantum yield calculated from the decay kinetics and the one measured directly shows that the majority of the azurin molecules are not fluorescent. There is thus variability in the structure of azurin molecules with an equilibration time that is longer than the fluorescence lifetime. Different asymmetric environment was found for the tryptophan residue in oxidized and reduced holoprotein and in apoazurin, as studied by the circular polarization of the fluorescence. D(2)O increases the fluorescence lifetime of apoazurin by 6 percent, compared to the lifetime in H(2)O solution; therefore water molecules may have access to the tryptophan residue, though the latter is situated in a hydrophobic environment.

Amides↗
PubMed1972

Evaluation of the distribution of distances between energy donors and acceptors by fluorescence decay.

When transfer of electronic excitation energy occurs between a donor-acceptor pair by the Förster mechanism, the decay of fluorescence of the donor follows first-order kinetics, with a rate constant that depends on the distance from donor to acceptor. In a system that contains donor-acceptor pairs of different separations, the fluorescence decay of the donors will not be exponential, but will depend on the distribution function of donor-acceptor distances, f(r). Various approaches are outlined for the extraction of information about f(r) from the decay curve of donor fluorescence. Specifically, if a plausible expression with adjustable parameters is assumed for f(r), numerical methods can be used to evaluate the parameters that yield the closest fit between the observed decay curve and that calculated from the assumed f(r). The technique of fluorescence decay may prove to be useful for determination of distribution functions of end-to-end distances of polymers to the edges of which suitable donor-acceptor chromophore pairs have been attached.

Journal Article↗
PubMedDate not supplied

Real-time optical imaging of naturally evoked electrical activity in intact frog brain.

A major obstacle to understanding the function and development of the vertebrate brain is the difficulty in monitoring dynamic patterns of electrical activity in the millesecond time domain; this has limited investigations of such phenomena as modular organization of functional units, seizure activities and spreading depression. The use of voltage-sensitive dyes and the recent development of the use of an array of photodiodes has provided a unique technique for monitoring the dynamic patterns of electrical activity in real time from a variety of invertebrate or vertebrate neuronal preparations including the rat cortex. In the present study, this technique has been used to investigate the intact optic tectum of the frog. We demonstrate that optical measurements can be used for real-time imaging of spatio-temporal patterns of neuronal responses and for identification of functional units evoked by natural visual stimuli. We report also the structure of the new voltage-sensitive probe that facilitates the in vivo applications of this technique.

Animals↗
PubMedDate not supplied

Functional architecture of cortex revealed by optical imaging of intrinsic signals.

Optical imaging of cortical activity offers several advantages over conventional electrophysiological and anatomical techniques. One can map a relatively large region, obtain successive maps to different stimuli in the same cortical area and follow variations in response over time. In the intact mammalian brain this imaging has been accomplished with the aid of voltage sensitive dyes. However, it has been known for many years that some intrinsic changes in the optical properties of the tissue are dependent on electrical or metabolic activity. Here we show that these changes can be used to study the functional architecture of cortex. Optical maps of whisker barrels in the rat and the orientation columns in the cat visual cortex, obtained by reflection measurements of the intrinsic signal, were confirmed with voltage sensitive dyes or by electrophysiological recordings. In addition, we describe an intrinsic signal originating from small arteries which can be used to investigate the communication between local neuronal activity and the microvasculature. One advantage of the method is that it is non-invasive and does not require dyes, a clear benefit for clinical applications.

Animals↗