Parallax method for direct measurement of membrane penetration depth utilizing fluorescence quenching by spin-labeled phospholipids

This report describes a method suitable for determining the depth of a wide variety of fluorescent molecules embedded in membranes. The method involves determination of the parallax in the apparent location of fluorophores detected when quenching by phospholipids spin-labeled at two different depths is compared. By use of straightforward algebraic expressions, the method allows calculation of depth in angstroms. Furthermore, the analysis can be extended to quenching by energy-transfer acceptors or brominated probes under appropriate conditions. Application of the method to quenching of 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD)-labeled lipids by spin-labeled lipids located at three different depths is demonstrated in model membranes. It is shown that the calculated depths of the NBD groups are self-consistent to the extent that they are the same no matter which two spin-labels have been used in a particular experiment. In addition, the calculated depth is independent of spin-label concentration in the membrane within +/- 1 A, ruling out major effects due to spin-label perturbation. The quenching experiments show that the location of the NBD group in head-group-labeled phosphatidylethanolamine is at the polar/hydrocarbon interface and that of an NBD label on the "tail" of cholesterol is deeply buried, as expected. Unexpectedly, NBD labels placed at the end of fatty acyl chains of phosphatidylcholines are also near the polar/hydrocarbon interface. Presumably, the polarity of the NBD group results in "looping" back to the surface of the NBD groups attached to flexible acyl chains.

Fluorimetric determination of critical micelle concentration avoiding interference from detergent charge

Upon mixing detergent solutions with the neutral fluorescent molecule 1,6-diphenyl-1,3,5-hexatriene a large increase in fluorescence is observed if detergent exceeds the critical micelle concentration. This property has been used to determine the critical micelle concentration of anionic, uncharged, zwitterionic, and cationic detergents. Regardless of detergent charge, the critical micelle concentrations obtained agree with the values obtained by other methods. This fluorescence assay is both sensitive and rapid, and should provide a simple and general method for determination of critical micelle concentration of any detergent.

Psychiatric presentations in rabies. A clinico-pathologic report from South India with a review of literature

Two atypical cases of rabies, mimicking respectively schizophrenic psychosis and acute manic excitement, are reported along with autopsy data. The importance to recognize these variants, particularly in rabies prevalent areas, is emphasized. The potential sources of diagnostic confusion are discussed, along with a review of the relevant literature.

Scalp hair as a monitor of community exposure to lead

Lead was measured by photon activation analysis in scalp hair from three population groups with varied types of environmental exposure. Concentrations of lead in hair increased from rural to urban to smelter areas with medians of 9.1, 15.3, and 48.5 ppm, respectively. Boys under 16 residing near smelters showed consistently higher lead levels than girls of the same age group and from the same area. A history of exposure to lead was deduced from the distribution of concentration along the hair length by analyzing 1-or 2-cm segments of hair strands. A reasonably good blood lead-hair lead correlation was obtained for individuals who appeared to be in a steady state with respect to intake and excretion of lead. The analytical method for the photonuclear determination of lead in hair, the hair washing procedure, and the advantages of using hair as an epidemiologic monitor are described.

Lead contamination around secondary smelters: estimation of dispersal and accumulation by humans

A high rate of lead fallout around two secondary lead smelters originated mainly from episodal large-particulate emissions from low-level fugitive sources rather than from stack fumes. The lead content of dustfall, and consequently of soil, vegetation, and outdoor dust, decreased exponentially with distance from the two smelters. Between 13 and 30 percent of the children living in the contaminated areas had absorbed excessive amounts of lead (more than 40 micrograms per 100 milliliters of blood and more than 100 micrograms per gram of hair) as compared with less than 1 percent in a control group. A relationship between blood and hair was established which indicated that the absorption was fairly constant for most children examined. It seemned that the ingestion of contaminated dirt and dusts rather than "paint pica" was the major route of lead intake. Metabolic changes were found in most of 21 children selected from those with excessive lead absorption; 10 to 15 percent of this group showed subtle neurological dysfunctions and minor psychomotor abnormalities.

Transposition of teeth and genetic etiology

Twenty-one cases of transposition are presented showing a crude prevalence of 0.4%. A high rate of bilateral occurrence was seen. A significant number of cases were associated with other dental anomalies, such as peg-shaped lateral incisors and overretained deciduous teeth. Genetic etiology has been stressed and various other theories discussed.