Hydrogen exchange in hydrated films of proteins. Application to the E. coli lac repressor core

An original easy method of hydrogen to deuterium exchange in hydrated films of proteins, followed by infrared absorption measurements, is described and applied to films of the E. coli lac repressor core, in order to examine the effect of isopropyl-beta-D-thiogalactoside (IPTG) binding. An estimation of about 25% alpha helical structure in this protein fragment is deduced from the exchange curve. The binding of IPTG to the core does not affect the exchange curve within the experimental error limits.

Fluorescence polarization studies of rat liver microsomes with altered phospholipid desaturase activities

Phospholipid desaturase activity of rat liver microsomes can be varied by dietary manipulation: rats starved and refed a "fat-free" diet have two to three times the activity of normal controls whereas starved rats have no detectable activity. These changes were accompanied by changes in fatty acid composition of the microsomal phospholipids, resulting in a double bond: saturated fatty acid mole ratio (moles double bonds per mole saturated fatty acid) of 5.7 in control and starved rats and 4.7 in starved-refed rats. Fluorescence polarization ratio P (I parallel/I perpendicular to x instrument correction factor) of cis- and trans-parinaric acid (PnA) showed no significant differences in physical state of the three microsomal preparations. However, the isolated microsomal phospholipids with trans-PnA as probe showed differences in the temperature at which onset of a change in polarization ratio occurred (starved-refed greater than normal greater than starved rats). With the cis-PnA as probe, the polarization ratio showed no change in the range 10-40 degrees C but was significantly higher (1.8) in starved-refed rats than in normal and starved rats (1.6 in both cases). These data indicate that the microsomal phospholipids of starved-refed animals were in a less fluid state than those from control and starved rats and that this decrease in fluidity was correlated with an increase in phospholipid desaturase activity.

Effect of sea-state on the performance of laser fluorosensors

The effect of the sea-state on the performance of laser fluorosensors operating in both spectral and temporal modes is estimated. For the spectral mode, calculations of the dependence of reflective losses on the angle of incidence show that the attenuation of the fluorescence return is not significantly affected for the range of sea-states expected in deep water. In the temporal mode the return signal is distorted by the sea-state. Fortuitously this distortion does not significantly alter the full width at half maximum (FWHM), a parameter from which decay times can be estimated.

Time-resolved laser fluorosensors: a laboratory study of their potential in the remote characterization of oil

The fluorescence decay profiles have been determined for a number of light, crude, and heavy oils under ideal laboratory conditions to assess their utility in the remote characterization and identification of oil spills using remote laser fluorosensors. The fluorescence decay of light and crude oils can best be described by double exponential kinetics with the former having longer. decay constants. The heavy oils are described by only a single exponential decay function with a lifetime less than 1 nsec.

Time resolved fluorescence of aqueous tryptophan

The fluorescence decay of aqueous tryptophan is shown to be described by a two exponential decay function whose components have life-times of 3.14 ns and 0.51 ns. These components are assigned as the solvent equilibrated 1La and 1Lb, states respectively. The time-resolved emission spectra are presented and can be resolved into two spectra with λmax at 350 nm and 335 nm corresponding to these two states.

Confidence in fluorescence lifetime determinations: a ratio correction for the photomultiplier time response with wavelength

The photomultipliers used in single photon counting fluorescence lifetime Systems have a time response function which varies with wavelength. This variation results in a reduced confidence in the kinetic parameters obtained after deconvolution of the lamp intensity decay profile measured at the excitation wavelength from the sample emission decay profile measured at the emission wavelength. Moreover in the case of multi-component decays, inaccurate kinetic parameters are calculated because of this PMT variation. Using weighted residual plots, we demonstrate how one may make a satisfactory subjective appraisal of the adequacy of the deconvolution and the physical model of the decay processes. We have developed a ratio correction technique which accounts for the PMT time response variation with wavelength. This technique requires no apriori assumption of the nature of the PMT effect. Only when the data are corrected using the ratio correction technique can sufficient confidence in the accuracy of the singlet excited state parameters and the validity of the physical model be obtained.

Cimicine and Cimicidine, Lactonic Alkaloids from Haplophyton cimicidum

Evidence is presented in support of the stereostructures 4 and 5 for cimicine and cimicidine, respectively. Alkaloids 4 and 5, as well as the lactonic bases aspidophytine (23) and haplophytine (1), are converted by alkaline hydrogen peroxide to the corresponding 10-oxo derivatives.

Triplet state of orotic acid and orotic acid methyl ester in solution

Flash photolysis of orotic acid and orotic acid methyl ester in aqueous solution was studied. The transients were identified as triplet excited states on the basis of their lifetimes, sensitization, quenching, and self-quenching experiments. The rate constants for self-quenching and for decay of the triplet were measured and discussed in terms of dimerization and competing unimolecular and pseudo-unimolecular processes. A triplet energy of 60 kcal mole−1 was deduced for both orotic acid and orotic acid methyl ester from triplet energy transfer measurements.

Detection and chemistry of the triplet state of thymine

The transient produced on flash excitation of degassed solutions of thymine in acetonitrile has been characterized as the triplet excited state of thymine. This triplet state has a lifetime of 14 ± 1 μs and the associated dimerization rate was found to be 5.3 ± 0.3 × 108 M−1 s−1. The triplet state of thymine could be quenched by 2,4-hexadien-1-ol with a rate constant of 8.1 ± 0.6 × 109 M−1 s−1.