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Biomedical subjects

S T Sun

Publications and source records attributed to S T Sun.

10 recordsLinked to original sources
PubMed1984

Direct observation of delta-crystallin accumulation by laser light-scattering spectroscopy in the chicken embryo lens.

By using the technique of laser light-scattering spectroscopy, direct observation has been made on the intracellular accumulation of a crystallin protein within the cells of chicken embryo lens during the process of development. Appearance of delta-crystallin has been detected as early as day 4, and its concentration reaches a plateau at day 19. The measurements constitute a noninvasive determination of accumulation of protein molecules that specifically characterize the process of cell differentiation.

Animals↗
PubMed1983

Hemoglobin aggregation in single red blood cells of sickle cell anemia.

A laser light scattering technique was used to observe the extent of hemoglobin aggregation in solitary red blood cells of sickle cell anemia. Hemoglobin aggregation was confirmed in deoxygenated cells. The light scattering technique can also be applied to cytoplasmic studies of any biological cell.

Anemia, Sickle Cell↗
PubMed1983

Phase separation in rat lenses cultured in low glucose media.

Experimental evidence that indicates the nuclear opacity that develops in the hypoglycemic cataract in rat lenses is the result of a phase separation of the lens cytoplasm is presented. Phase diagrams of the cytoplasm of organ-cultured lenses were constructed for a series of incubation times in normal and hypoglycemic media. In normal media, the maximum phase separation temperature, Tmax, of the lens cytoplasm decreases with time. In hypoglycemic media, Tmax increases with time and exceeds 37 C after 24 hrs. The increase in Tmax can be stopped and reversed if the lens is returned to normal media within 8 hrs; in good agreement with an earlier biochemical analysis of the kinetics of hypoglycemic cataract formation.

Animals↗
PubMed1979

Fusion of phosphatidylserine and mixed phosphatidylserine-phosphatidylcholine vesicles. Dependence on calcium concentration and temperature.

Dynamic light scattering has been used to study the temperature dependence of Ca2+-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca2+ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca2+ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca2+ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca2+ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca2+, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca2+ concentration, and identical to that with pure phosphatidylserine in excess Ca2+. The results imply that Ca2+- induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains.

Calcium↗
PubMed1979

Cytoplasmic phase separation in formation of galactosemic cataract in lenses of young rats.

We have determined the age dependence of the characteristics of the cytoplasmic phase separation of lenses from normal and galactosemic young rats. In the normal lens, the temperature at which the phase separation occurs decreases monotonically with age. In the lenses of rats fed with a high galactose diet, the phase separation temperature becomes increasingly higher with the development of galactosemia. When the phase separation temperature becomes higher than the ocular temperature, the nuclear opacity appears in vivo. The opacity is the result of light scattering by spatial fluctuations of the refractive index formed by interspersed regions of two separated phases in the fiber cell cytoplasm. This shows that the nuclear opacity that develops in the lens of galactosemic rats is the manifestation of phase separation of the lens fiber cytoplasm.

Journal Article↗
PubMed1978

Temperature dependence of calcium-induced fusion of sonicated phosphatidylserine vesicles.

We have measured the temperature dependence calcium-induced fusion of sonicated phosphatidylserine vesicles. The vesicles were incubated in the presence of calcium at a specified temperature until the resulting aggregation or fusion process had gone to completion. EDTA was then added and the resulting final size of the vesicle population was measured by using dynamic light scattering. This final size was plotted against incubation temperature to show the temperature dependence of calcium-induced fusion. This curve has a peak near 11 degrees C which may be associated with the phase transition of the sonicated phosphatidylserine vesicles in the presence of calcium prior to the aggregation or fusion process.

Animals↗
PubMed1977

Dynamic light scattering study of calcium-induced fusion in phospholipid vesicles.

Acidic sonicated phospholipid vesicles can undergo dramatic morphological changes due to fusion in the presence of divalent metal ions. For example, small spherical phosphatidylserine vesicles can form scroll-like cylinders which precipitate in the presence of Ca2+ above a threshold concentration. Subsequent addition of EDTA will yield large, unilamellar vesicles. These events have previously been established through the combined use of differential scanning calorimetry and freeze-fracture electron microscopy. We have applied the technique of dynamic light scattering to follow these fusion events rapidly, accurately, and non-perturbatively as they occur in solution at calcium concentrations slightly below threshold for precipitation.

Calcium↗