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PubMed1991

Position-dependent local motions in spin-labeled analogues of a short alpha-helical peptide determined by electron spin resonance.

We have used electron spin resonance and circular dichroism to examine and compare the dynamics in two analogues of the Ala-based 3K(I) peptide [Marqusee, S., Robbins, V.H., & Baldwin, R. L. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 5286-5290], labeled at positions 4 and 8, throughout the alpha-helix----coil transition. In the middle of the thermal unfolding transition, our results demonstrate that the local mobility near the N-terminus is greater than at the center of the peptide. This provides evidence, from the perspective of dynamics, that the ends of Ala-based alpha-helices are frayed. We further find that the position dependence of the mobility for the thermally unfolded state differs from that of the denaturant unfolded state. Only the latter state exhibits the local dynamics expected for a genuine random coil.

Alanine↗
PubMed1998

Rotational dynamics of spin-labelled surfactant-associated proteins SP-B and SP-C in dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol bilayers.

Pulmonary surfactant proteins SP-B and SP-C have been isolated from porcine lungs and selectively labelled with 2,2,6, 6-tetramethylpiperidine-N-oxyl (TEMPO)-isothiocyanate at their N-terminal amine ends, to analyse the mobility of both proteins on the nanosecond time scale using electron spin resonance (ESR) spectroscopy. Reconstitution of the labelled forms of these proteins in bilayers of dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG) results in much broader and anisotropic ESR spectra, indicating a large restriction in rotational mobility of the protein-attached probe when inserted in membranes. Distinctive differences were found between the ESR spectra of the two polypeptides, that were consistent with intrinsic differences in mode of interaction of SP-B and SP-C with phospholipid bilayers. The mobility of the protein spin probes was sensitive to temperature on the time scale of conventional spin-label ESR. Both proteins, TEMPO-SP-B and TEMPO-SP-C, showed considerable increases in mobility at temperatures above the pretransition of pure DPPC. Finally, the mobility of the spin probes attached to both SP-B and SP-C was more restricted in DPPG than in DPPC bilayers, demonstrating that electrostatic interactions of the positively charged residues at the protein surface influence the rotational dynamics of the proteins in anionic lipid bilayers. Although some residual segmental mobility of the thiourea-linked probes cannot be discounted, the results clearly reflect preferential differences in overall protein dynamics in gel and fluid phases of the two phospholipids that could be important for the biophysical properties of surfactant bilayers and monolayers.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1987

Tyrosinase-catalyzed oxidation of dopa and related catechol(amine)s: a kinetic electron spin resonance investigation using spin-stabilization and spin label oximetry.

The oxidation of four catechol(amine)s by tyrosinase has been studied by electron spin resonance and optical methods. Rates of oxygen consumption and of dopaquinone and dopachrome formation during the oxidation of dopa have been measured, and compared with rates of dopasemiquinone production measured using spin-stabilization procedures. In the presence of spin-stabilizing metal ions, production of semiquinone is approximately quantitative. Time-dependent ESR spectra obtained from dopa and dopamine show a slow regeneration of semiquinone, suggesting that a semiquinone precursor is slowly reformed. In contrast, time-dependent spectra for 4-methylcatechol and N-acetyldopamine show decay of the primary semiquinone together with buildup of a secondary semiquinone apparently derived from the corresponding 6-hydroxy-catechol(amine). Thus, catecholamines that give rise to a cyclizable quinone show a pattern of behavior that differs from those that produce a non-cyclizable quinone. These results are discussed in terms of their possible significance to melanogenesis and the toxicity of catechol(amine)s, which has been attributed to production of semiquinones and/or other oxygen radicals.

Benzoquinones↗
PubMedDate not supplied

[Spin label study of plasma lipoproteins].

Lipoprotein structure was studied by means of EPR-spectroscopy of spin probes--iminoxyl derivatives of stearic acid and of androstane--in blood plasma of 40-59 years old men. The mode of wrapping of external monolayer of lipoprotein particles, the type of their intermolecular interactions were similar to corresponding characteristics of bilayer in biological and model membranes. Correlation was observed between concentration of separate lipoproteins in blood plasma and the structural parameters of the probe distribution in hydrophobic and polar regions of the lipoprotein preparations. The phenomena observed might be related to capacity of the high density lipoproteins to accept cholesterol from cell membranes with transfer of cholesterol into liver tissue, where it is subsequently metabolized, as well as to the property of the very low density lipoproteins to transfer cholesterol into tissues, particularly, into vascular walls.

Adult↗
PubMed1990

Effect of hyperthermia on the internal microviscosity of erythrocytes and lymphocytes: a spin-label study.

The internal microviscosity of human erythrocytes and porcine lymphocytes was investigated, from the electron-spin resonance spectral characteristics of the nitroxyl spin probe, 4-amino-2,2,6,6-tetramethylpiperidinyloxy. Heat-induced permanent damage to cells was observed as an increase in the intracellular microviscosity of nucleate and enucleate cells. Induction of heat resistance was found for erythrocytes treated with a double heat shock.

Animals↗
PubMed1982

Investigation of membrane structure using fluorescence quenching by spin-labels. A review of recent studies.

Fluorescence quenching is the loss of fluorescence intensity which is observed when a fluorescent molecule or group interacts with another molecule or group, called the quencher. By use of tryptophan residues of proteins, together with specific probe molecules, quenching can be applied to problems of biological and model membrane structure. Quenching interactions are short range (less than 50 A) so that structure on the scale of molecular dimensions can be examined. This review summarizes the recent applications of fluorescence quenching by spin (nitroxide)-labeled molecules to problems of membrane structure, including determination of the distance of membrane-bound molecules from the membrane surface, the strength of lipid-protein interactions and the strength of protein-protein interactions within membranes. The unique advantages and the limitations of this powerful method are examined.

Animals↗
PubMed1988

Use of membrane spin label spectra to monitor rates of reaction of partitioning compounds: hydrolysis of a local anesthetic analog.

ESR spectra of membrane spin probes are conventionally used to obtain structural information. Here we show, for the first time, that when a membrane-soluble compound undergoes a chemical reaction, time-dependent changes in the ESR spectra of membrane spin probes can yield information about the kinetics of reaction. A benzoic acid ester, analog of the local anesthetic tetracaine, partitions between aqueous and membrane phases, causing changes in membrane structure as monitored by the ESR spectra of a probe. At alkaline pH, the lineshapes are time-dependent and the spectra go back to that in the absence of drug. The changes follow pseudo-first order kinetics. This effect is due to drug hydrolysis leading to water-soluble products, as confirmed by direct spectrophotometric measurements of the reaction. The pseudo-first order rate constants found by the latter method are in very good agreement with those calculated by ESR. The rate of hydrolysis decreases with increasing membrane concentration. This phenomenon accounts in part for the increased potency and toxicity of the more membrane-soluble local anesthetics.

Cyclic N-Oxides↗