Quantitative determination of conformational disorder in the acyl chains of phospholipid bilayers by infrared spectroscopy

A method is proposed and demonstrated for the direct determination of conformational disorder (trans-gauche isomerization) as a function of acyl-chain position in phospholipid bilayer membranes. Three specifically deuterated derivatives of dipalmitoylphosphatidylcholine (DPPC), namely 4,4,4',4'-d4-DPPC (4-d4-DPPC), 6,6,6',6'-d4-DPPC (6-d4-DPPC), and 10,10,10',10'-d4-DPPC (10-d4-DPPC), have been synthesized. The CD2 rocking modes in the Fourier transform infrared (FT-IR) spectrum have been monitored as a function of temperature for each derivative. A method originally applied by Snyder and Poore [(1973) Macromolecules 6, 708-715] as a specific probe of hydrocarbon chain conformation in alkanes has been used to analyze the data. The rocking modes appear at 622 cm-1 for a CD2 segment surrounded by a trans C-C-C skeleton and between 645 and 655 cm-1 for segments surrounded by particular gauche conformers. The integrated band intensities of these modes have been used to monitor trans-gauche isomerization in the acyl chains at particular depths in the bilayer. At 48 degrees C, above the gel-liquid-crystal phase transition, the percentage of gauche rotamers present is 20.7 +/- 4.2, 32.3 +/- 2.3, and 19.7 +/- 0.8 for 4-d4-DPPC, 6-d4-DPPC, and 10-d4-DPPC, respectively. The gel phase of the latter two molecules is highly ordered. In contrast, a substantial population of gauche rotamers was observed for the 4-d4-DPPC. The conformational analysis yields a range of 3.6-4.2 gauche rotamers/acyl chain of DPPC above the phase transition. This range is in excellent accord with the dilatometric data of Nagle and Wilkinson [(1978) Biophys. J. 23, 159-175]. The significant advantages of the FT-IR approach are discussed.     

An anchored molecular map of mouse Chromosome 6 with an analysis of interference

The haplotype data reported in this paper have been submitted to (MGD) and have been assigned the accession numbers: MGD-CREX-235 (back-cross data); MGD-CREX-236 (intercross data).     

MSCs—cells with many sides

The field of mesenchymal stromal cell (MSC) biology and clinical cellular therapy has grown exponentially over the last few decades. With discovery of multiple tissue specific sources of stromal cells, invariably being termed MSCs, and their increasing clinical application, there is a need to further delineate the true definition of a mesenchymal stromal cell and to recognise the inherit differences between cell sources; both their potential and limitations.In this review, we discuss the importance of considering every stromal cell source as an independent entity and the need to critically evaluate and appreciate the true phenotype of these cells and their safety when considering their use in novel cell therapies.