An extended kinetic analysis of valinomycin-induced Rb-transport through monoglyceride membranes

Summary The time course of the current following a voltage jump, which is applied to monoglyceride bilayers in the presence of valinomycin, shows two relaxation times. This is basically in agreement with a simple carrier model which has been described in full detail formerly. Relaxation times and amplitudes allow a calculation of the rate constants of the transport model. The presented data supplement an analysis which was hitherto based only on the slower relaxation process and on information derived from the nonlinearity of currentvoltage characteristics. The additional resolution of the faster relaxation time allowed an approximate determination of the voltage dependence of the translocation rate constant for the carrier-ion-complex and provided evidence for a small voltage dependence of the interfacial reaction. The dependence of the relaxation parameters on the ion concentration in the aqueous phase was interpreted assuming a saturation of the ion concentration at the reaction plane at high bulk concentrations.     

Metabolism of Ethionine in Ethionine-Sensitive and Ethionine-Resistant Cells of the Enteric Yeast Candida slooffii

In a defined medium with added ethionine plus low methionine, phenylalanine, tryptophan, tyrosine, adenine, and additional methionine reversed inhibition of the enteric yeast Candida slooffii by ethionine. Isoleucine and 7-methylguanine restored half-maximal growth. Choline but not triethylcholine inhibited C. slooffii. 6-Mercaptopurine reversed ethionine inhibition and also synergistic inhibition by ethionine plus choline. Protection against ethionine by adenine plus aromatics was also evident with log-phase cells in the absence of methionine. Incorporation of ethionine-ethyl-1-(14)C by resting cells was partially inhibited by aromatic amino acids and methionine. Ethionine depressed incorporation of (3)H-phenylalanine but not of (3)H-adenine. Ethionine-resistant mutants were isolated which incorporated ethionine efficiently and degraded it to yet unidentified substances not including 5'-ethylthioadenosine. Ethionine-sensitive cells accumulated more S-adenosylethionine (SAE) than resistant mutants. Adenine was a good precursor of SAE. Radioactivity from ethionine-ethyl-1-(14)C was recovered from cell fractions of ethionine-sensitive cells with the following distribution: cold trichloroacetic acid-soluble > hot trichloroacetic acid-insoluble > lipids > deoxyribonucleic acid > ribonucleic acid. Total radioactivity recovered from ethionine-sensitive cells was twice as much as that from ethionine-resistant mutants.     

Computer simulation of overshoot in saccadic eye movements.

The human horizontal eye movement system produces quick, precise, conjugate eye movements called saccades. These are important in normal vision. For example, reading tasks exclusively utilize saccadic eye movements. The majority of saccades have dynamic overshoot. The amplitude of this overshoot is independent of saccadic amplitude, and is such that it places the image of the stimulus within the retinal region of maximum acuity within a minimum of time. A computer based model of the saccadic mechanisms was used to study the origin of this overshoot. It was discussed that dynamic overshoot cannot be attributed to biomechanism properites of the eye movement mechanism, but must instead be explained by variations in the controlling nervous activity. The form of this neural controller signal is very similar to that required for a time optimal response of an inertial system.     

Release of template restriction for DNA synthesis by poly ADP(ribose) polymerase during the HeLa cell cycle.

The degree of complexing between DNA and chromosomal proteins and the ability of poly adenosine diphosphate ribosylation (ADP-ribosylation) of nuclear proteins to release this template restriction and expose DNA primer site changes during the HeLa cell cycle. Primer site exposure by NAD and poly ADP(ribose) polymerase was assessed with intact nuclei by single deoxynucleotide incorporation into DNA in the presence of saturating bacterial DNA polymerase. The most marked in vitro enhancement of primer site exposure by ADP-ribosylation occurred in early G1 phase, where cellular template restriction was the greatest. Cytoplasmic DNA polymerase also had high activity in early G1 phase of the cell cycle. Streptozotocin reduces NAD pools in HeLa cells; a concomitant stimulation of nuclear poly ADP(ribose) polymerase activity is noted.     

Immunofluorescent Detection of Enterotoxin B in Food and a Culture Medium

Both Staphylococcus aureus strains 243 and S-6 cells producing enterotoxin B and free enterotoxin in food and culture medium were rapidly demonstrated by using the fluorescent-antibody technique. Comparison of cell fluorescence and enterotoxin B production determined by double gel diffusion showed that an estimation of enterotoxin production could be made by observing the degree of cell fluorescence. The fluorescent-antibody technique was used to determine whether cells were producing enterotoxin under varying nutritional and environmental conditions: NaCl concentration, culture aeration, and time and temperature of incubation in Brain Heart Infusion broth and shrimp slurries. At the various NaCl concentrations, the fluorescence of cells was found positively associated with enterotoxin B production only during the first 12 hr of growth. As the NaCl concentration was increased from 0 to 10%, the fluorescence of cells and toxin production decreased. Maximum for cell fluorescence and enterotoxin production was observed at 37 C. Little or no difference in cell fluorescence and enterotoxin production with both strains was found between Brain Heart Infusion broth and shrimp slurry cultures. All results obtained with the fluorescent-antibody technique were verified with double gel diffusion for enterotoxin detection and quantitation.     

Separation of apolipoprotein B species by agarose-acrylamide gel electrophoresis

Human apolipoprotein (apo) B has been recognized to exist in two different forms designated apoB-100 and apoB-48. The two apoB forms are usually separated by NaDodSO4 gel electrophoresis with a low percentage polyacrylamide gel in a tube gel apparatus. However, the matrix of this low percentage gel is relatively weak, and one can separate the two forms of apoB in a slab gel apparatus only if one utilizes a gradient polyacrylamide gel or a higher percentage polyacrylamide gel which results in a poorer separation of the protein bands. We have developed an agarose-acrylamide gel electrophoretic method to separate the two major apoB forms. The gel is a mixture of 0.5% agarose and 2% acrylamide. The agarose-acrylamide method is fast, has the advantage of being able to be used on an analytical or preparative scale in a vertical slab gel apparatus, and the gel is of sufficient strength to be used in immunoblotting and/or radioautography.