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Biomedical subjects

T G Anderson

Publications and source records attributed to T G Anderson.

5 recordsLinked to original sources
PubMed2000

Condensed complexes, rafts, and the chemical activity of cholesterol in membranes.

Epifluorescence microscopy studies of mixtures of phospholipids and cholesterol at the air-water interface often exhibit coexisting liquid phases. The properties of these liquids point to the formation of "condensed complexes" between cholesterol and certain phospholipids, such as sphingomyelin. It is found that monolayers that form complexes can incorporate a low concentration of a ganglioside G(M1). This glycolipid is visualized by using a fluorescently labeled B subunit of cholera toxin. Three coexisting liquid phases are found by using this probe together with a fluorescent phospholipid probe. The three liquid phases are identified as a phospholipid-rich phase, a cholesterol-rich phase, and a condensed complex-rich phase. The cholera toxin B labeled ganglioside G(M1) is found exclusively in the condensed complex-rich phase. Condensed complexes are likely present in animal cell membranes, where they should facilitate the formation of specialized domains such as rafts. Condensed complexes also have a major effect in determining the chemical activity of cholesterol. It is suggested that this chemical activity plays an essential role in the regulation of cholesterol biosynthesis. Gradients in the chemical activity of cholesterol should likewise govern the rates and direction of intracellular intermembrane cholesterol transport.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2000

Miscibility critical pressures in monolayers of ternary lipid mixtures.

When phospholipids are mixed with cholesterol in a monolayer at an air-water interface, coexisting 2-dimensional liquid phases can be observed if the surface pressure, pi, is lower than the miscibility critical pressure, pi(c). Ternary mixtures of two phospholipid species with dihydrocholesterol have been reported to have critical pressures that are linearly proportional to the relative composition of the phospholipids. However, we report here that, if the acyl chains of the two phospholipids differ significantly in length or unsaturation, the behavior is markedly different. In this case, the critical pressure of the ternary mixture can be remarkably high, exceeding the critical pressures of the corresponding binary mixtures. High critical pressures are also seen in binary mixtures of phospholipid and dihydrocholesterol when the two acyl chains of the phospholipid differ sufficiently in length. Using regular solution theory, we interpret the elevated critical pressures of these mixtures as an attractive interaction between the phospholipid components.

Biophysical Phenomena↗
PubMed1999

Interpretation of biphasic dissociation kinetics for isomeric class II major histocompatibility complex-peptide complexes.

Antigenic peptides bound to class II major histocompatibility complex (MHC) proteins play a key role in the distinction between "self" and "nonself" by the cellular immune system. Although the formation and dissociation of these complexes are often thought of in terms of the simple mechanism [formula in text], studies of MHC-peptide dissociation kinetics suggest that multiple interconverting forms of the bound MHC-peptide complex can be formed. However, the precise relationship between observed dissociation data and proposed multiple-complex mechanisms has not been systematically examined. Here we provide a mathematical analysis to fill this gap and attempt to clarify the kinetic behavior that is expected to result from the proposed mechanisms. We also examine multiple-complex dynamics that can be "hidden" in conventional experiments. Although we focus on MHC-peptide interactions, the analysis provided here is fully general and applies to any ligand-receptor system having two distinct bound states.

Histocompatibility Antigens Class II↗