Fluorescence polarization detector for the computation of the degree of polarization P

A device has been designed and constructed which when used with a commercial fluorimeter allows the computation of the degree of polarization P on a time shared basis.     

Altering the association properties of insulin by amino acid replacement

The importance of Pro^B28 and Lys^B29 on the self-associationof insulin was established by systematically truncating theC terminus of the B chain. The relationship between structureand association was further explored by making numerous aminoacid replacements at B²⁸ and B²⁹ Association was studied bycircular dichroism, size-exclusion chromatography and ultracentrifugation.Our results show that the location of a prolyl residue at B²⁸is critical for high-affinity self-association. Removal of Pro^B28in a series of C-terminal truncated insulins, or amino acidreplacement of Pro²⁸, greatly reduced association. The largestdisruption to association was achieved by replacing Lys^B29 withPro and varying the amino acid at B²⁸ Several of the analogswere predominantly monomers in solutions up to 3 mg/ml. Theseamino acid substitutions decreased association by primarilydisrupting the formation of dimers. Such amino acid substitutionsalso substantially reduced the Zn-induced insulin hexamer formation.The formation of monomeric insulins through amino acid replacementswas accompanied by conformational changes that may be the causefor decreased association. It is demonstrated that self-associationof insulin can be drastically altered by substitution of oneor two key amino acids.     

Scattering of diffuse photon density waves by spherical inhomogeneities within turbid media: analytic solution and applications

We present an analytic solution for the scattering of diffuse photon density waves by spherical inhomogeneities within turbid media. The analytic result is compared to experimental measurements. Close agreement between theory and experiment permits the use of the theory to determine the properties of unknown sphere-like objects embedded in turbid media. The analytic solution is extended to encompass several problems of practical interest in imaging, including the influence of multiple sources, multiple objects, and boundaries on the characterization of spherical inhomogeneities. We also extend the solution to encompass time-domain measurements.     

The role of mobile organic radicals and ions (solitons,polarons and bipolarons) in the transport properties of doped conjugated polymers

We discuss the formation of charged defects such as solitons, polarons and bipolarons, in doped conjugated polymers. We present the results of ab initio quality calculations on the modifications of geometric and electronic structures occurring upon doping. A transport model for spinless conduction through bipolarons applicable to doped polymers with or without degenerate ground state is described.     

Cutaneous leishmaniasis in the Libyan Arab Republic: distribution of the disease and identity of the parasite

When mammalian sperm cells are exposed to solutions of albumin there are changes in the membranes of some species that resemble those that normally occur in the uterus prior to fertilization. We have shown that albumin molecules absorb on to the membranes of ejaculated rabbit sperm cells, and that the equilibrium binding constant, K, (1) varies inversely with the albumin concentration, (2) is independent of the sperm cell concentration in the range of 10(6)--10(7) per ml, (3) is independent of the time of exposure of the sperm cells to the albumin solution, and (4) decreases in the presence of Ca++ and Mg++ ions. An unusual aspect of the adsorption is that if the albumin concentration is given the symbol [A], K[A] is a constant in our measurements. This means that for virtually the entire range of [A] studied, the sperm cells bind albumin so that half of the available surface is coated and half remains uncoated. This situation is rather remarkable and it suggests a role that adsorption could play in the physical processes preceding fertilization. In purely physical systems, the optimum for the bridging and flocculation of particles that are coated with adsorbed macromolecular films occurs when half of the available surface is covered. The sperm cell appears to provide the optimal situation for interacting with itself or with another surface.     

Standoff detection of high explosive materials at 50 meters in ambient light conditions using a small Raman instrument

We have designed and demonstrated a standoff Raman system for detecting high explosive materials at distances up to 50 meters in ambient light conditions. In the system, light is collected using an 8-in. Schmidt-Cassegrain telescope fiber-coupled to an f/1.8 spectrograph with a gated intensified charge-coupled device (ICCD) detector. A frequency-doubled Nd : YAG (532 nm) pulsed (10 Hz) laser is used as the excitation source for measuring remote spectra of samples containing up to 8% explosive materials. The explosives RDX, TNT, and PETN as well as nitrate- and chlorate-containing materials were used to evaluate the performance of the system with samples placed at distances of 27 and 50 meters. Laser power studies were performed to determine the effects of laser heating and photodegradation on the samples. Raman signal levels were found to increase linearly with increasing laser energy up to approximately 3 x 10(6) W/cm2 for all samples except TNT, which showed some evidence of photo- or thermal degradation at higher laser power densities. Detector gate width studies showed that Raman spectra could be acquired in high levels of ambient light using a 10 microsecond gate width.     

Radiolytic modification and reactivity of amino acid residues serving as structural probes for protein footprinting

Hydroxyl radical-mediated protein footprinting is a convenient and sensitive technique for mapping solvent-accessible surfaces of proteins and examining the structure and dynamics of biological assemblies. In this study, the reactivities and tendencies to form easily detectable products for all 20 (common) amino acid side chains along with cystine are directly compared using various standards. Although we have previously reported on the oxidation of many of these residues, this study includes a detailed examination of the less reactive residues and better defines their usefulness in hydroxyl radical-mediated footprinting experiments. All 20 amino amides along with cystine and a few tripeptides were irradiated by gamma-rays, the products were analyzed by electrospray mass spectrometry, and rate constants of modification were measured. The reactivities of amino acid side chains were compared based on their loss of mass spectral signal normalized to the rate of loss for Phe or Pro that were radiolyzed simultaneously to serve as internal standards. In this way, accurate quantitation of relative rates could be assured. A reactivity order of amino acid side chains was obtained as Cys > Met > Trp > Tyr > Phe > cystine > His > Leu, Ile > Arg, Lys, Val > Ser, Thr, Pro > Gln, Glu > Asp, Asn > Ala > Gly. Ala and Gly are far too unreactive to be useful probes in typical experiments and Asp and Asn are unlikely to be useful as well. Although Ser and Thr are more reactive than Pro, which is known to be a useful probe, their oxidation products are not easily detectable. Thus, it appears that 14 of the 20 side chains (plus cystine) are most likely to be useful in typical experiments. Since these residues comprise approximately 65% of the sequence of a typical protein, the footprinting approach provides excellent coverage of the side-chain reactivity for proteins.     

Undersampling correction for array detector-based satellite spectrometers

Array detector-based instruments are now fundamental to measurements of ozone and other atmospheric trace gases from space in the ultraviolet, visible, and infrared. The present generation of such instruments suffers, to a greater or lesser degree, from undersampling of the spectra, leading to difficulties in the analysis of atmospheric radiances. We provide extended analysis of the undersampling suffered by modern satellite spectrometers, which include the Global Ozone Monitoring Experiment, Scanning Imaging Absorption Spectrometer for Atmospheric Chartography, Ozone Monitoring Instrument, and Ozone Mapping and Profiler Suite. The analysis includes basic undersampling, the effects of binning into separate detector pixels, and the application of high-resolution Fraunhofer spectral data to correct for undersampling in many useful cases.