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R V Mustacich

Publications and source records attributed to R V Mustacich.

6 recordsLinked to original sources
PubMed1978

Ligand-promoted transfer of proteins between phases: spontaneous and electrically helped.

A model system for the partitioning of peripheral membrane proteins into membranes by ligand binding has been examined experimentally. Both bovine serum albumin and lysozyme partition between water and 1-butanol by the addition of sodium p-toluene sulfonate at pH 2.4. The partitioning is characterized by high orders of reaction: 25 and 10, respectively. Theory indicates that these high orders of reaction need not result from cooperative ligand binding in either phase, but depend primarily upon the number N of protein sites at which the transfer-promoting ligant binds, and on the difference in free energy of formation delta F0s of the protein--ligand complexes in the two phases. From the reaction orders and the experimental values of N, 80 for albumin and 11 for lysozyme, delta F0s was calculated to be --0.5 kcal/mol (--2.1 kJ/mol) and --0.8 kcal/mol (--2.5 kJ/mol) per ligand bound, respectively. Experiments measuring the dependence on ligand concentration of the rate of protein electrophoresis across the water/butanol interface are described. These rates increase by more than two orders of magnitude as the ligand concentration approaches the critical value for partition and are inversely dependent on the number of ligant sites for the two proteins studied.

Ligands↗
PubMed1977

Velocity distributions of the streaming protoplasm in Nitella flexilis.

Laser light is Doppler-shifted in frequency by the streaming endoplasm of living cells of Nitella flexilis. The frequency spectrum of the scattered light can be interpreted as the histogram of velocities within the organism, with the exception of the intense low-frequency portion of the spectrum. We demonstrate that the lowest-frequency component is the result of amplitude modulation of the scattered light by the array of chloroplasts in the cell. Measurement of the streaming endoplasm in a photobleached "window" region allows correction of the frequency distribution for the modulation component. The complete velocity histogram for the streaming endoplasm is calculated directly from the corrected frequency distribution. Measurements of vacuolar and endoplasmic motions show that the tonoplast, the membrane separating the vacuole and the endoplasm, seems to be flowing along with the endoplasm and vacuolar sap. Placing the cell in medium containing ATP in concentrations greater than 10(-3) M greatly increases the contribution of low velocities to the velocity histogram. Cytochalasin B at high dosages (10-50 mug/ml) does not noticably change the shape of the velocity histogram, while at low dosages (1 mug/ml) there is an increase in the contribution of low velocities to the velocity histogram. Colchicine in high concentrations (1%) has no observable effect on the velocity histogram.

Adenosine Triphosphate↗
PubMed1976

A study of protoplasmic streaming in Nitella by laser Doppler spectroscopy.

Laser light scattered from particles in the streaming protoplasm of a living cell is shifted in frequency by the Doppler effect. The spectrum of the scattered light can be measured and interpreted to infer details of the velocity distribution in the protoplasm. We have developed this approach to study the protoplasmic streaming in the fresh-water alga Nitella. Our results indicate a characteristic flow pattern to which diffusion makes a negligible contribution. No difference in the velocity of particles of different size is indicated. The streaming velocity linearly with temperature with a supraoptimal temperature of 34 degrees C, and the velocity distribution becomes narrower at high temperatures. The protoplasmic streaming can be inhibited by laser light, and this effect has been used to study the photoresponse of the algae. Using beam diameters of about 50 mum, we have shown that the inhibition is very local, becoming minimal at a displacement of about 200 mum in the upstream direction and 400 mum in the downstream direction. Prolonged exposure produces a bleached area free of chloroplasts, which is three orders of magnitude less sensitive to photoinhibition.

Chlorophyta↗