A model for oscillating chemical reactions.

A simple theoretical model for a class of oscillating chemical reactions is investigated, which is inspired by Degn's analysis of the mechanism of Belousov-Zhabotinsky reactions. Although the model involves only one auto-catalytic path, as distinct from models presented hitherto, a limit-cycle behaviour is found for the concentrations, corresponding to a definite region in the space of controllable parameters. Characteristics of the coherent oscillations are investigated together with the behaviour in the induction period. The critical slowing-down around the onset of instability is shown to behave very much like that found in the equilibrium phase transition. The existence of an "anti-Curie" point is found as well as the Curie point, corresponding to the fact that the domain for sustained oscillation is closed in certain directions. Possible extensions of the model and ways of improving the theory are discussed.     

A new-generation apparatus for studying memory-related performance in mice

1. We developed a new kind of food search test that can measure murine nocturnal memory without handling hard work for setting up.2. This apparatus has four food stations, but only one station had accessible food at any time. The one station with accessible food was changed at 4-h intervals.3. We compared the performance of transient forebrain global Ischemic mice, which are a hippocampal lesion model, with the performance of control C57BL/6J mice.4. The correct visit ratio, i.e., the ratio of the number of visits to the correct food station to the number of visits to all stations, gradually increased in the control mice, but did not change in the Ischemic mice.5. This new system was demonstrated to be an additional and useful tool for studying memory-related performance in mice.     

Rapid melting apparatus for studying thermal denaturation of polynucleotides.

A spectrophotometer attachment is described which allows complete thermal denaturation of heating/cooling cycles (0 to 90 to 0°C) of polynucleotides to be obtained in less than 5 min. Solutions with a wide range of optical densities (0.15 to 500) can be studied and several examples are given to demonstrate the performance and application of the device.     

Leakage-free rapid quenching technique for yeast metabolomics

Accurate determination of intracellular metabolite levels requires reliable, reproducible techniques for sampling and sample treatment. Quenching in 60% (v/v) methanol at −40°C is currently the standard method for sub-second arrest of metabolic activity in microbial metabolomics but there have been contradictory reports in the literature on whether leakage of metabolites from the cells occurs. We have re-evaluated this method in S. cerevisiae using a comprehensive, strictly quantitative approach. By determining the levels of a large range of metabolites in different sample fractions and establishing mass balances we could trace their fate during the quenching procedure and confirm that leakage of metabolites from yeast cells does occur during conventional cold methanol quenching, to such an extent that the levels of most metabolites have been previously underestimated by at least twofold. In addition, we found that the extent of leakage depends on the time of exposure, the temperature and the properties of the methanol solutions. Using the mass balance approach we could study the effect of different quenching conditions and demonstrate that leakage can be entirely prevented by quenching in pure methanol at ≤−40°C, which we propose as a new improved method. Making use of improved data on intracellular metabolite levels we also re-evaluated the need of sub-second quenching of metabolic activity and of removing the extracellular medium. Our findings have serious implications for quantitative metabolomics-based fields such as non-stationary ¹³C flux analysis, in vivo kinetic modeling and thermodynamic network analysis.

A continuous wave laser T-jump apparatus and its application to chemical reactions in hemoglobin single crystals

A laser temperature jump apparatus is constructed where the T-jump is achieved by means of the direct absorption of continuous laser radiation of low intensity by a solid sample. The final temperature in the irradiated volume element is reached when the absorbed radiation power equals the dissipation of heat by heat conduction. The time range from the beginning of irradiation to the stationary state depends on the geometry of the irradiated volume element and is less than 10 ms. The heating laser beam is simultaneously used to detect the relaxation to the new chemical equilibrium in the sample. Relaxation processes with relaxation rates between 10(2) s-1 and less than 10(-3) s-1 on samples with volumes less than 10(-3) mm3 may be investigated using this T-jump method. One application of this method is the determination of reaction rates of ligand reactions in hemoglobin single crystals. Rate constants obtained for the reaction of thiocyanate with crystallized horse methemoglobin are presented.     

A rapid, sensitive mass spectrometric method for investigating microscale chemical reactions of surface adsorbed peptides and proteins

A new mass spectrometric method for measuring the products of reactions of surface adsorbed peptides and proteins is described. The technique is rapid, convenient, and sensitive and provides detailed information concerning the molecular weights of the reaction products and the rate and extent of reaction. The properties of the technique are illustrated by an investigation of cleavage reactions of the disulfide bonds in bovine insulin, cyclic somatostatin, and conotoxin G1 utilizing the reducing agent dithiothreitol.     

Pyrimidine-specific chemical reactions useful for DNA sequencing.

Potassium permanganate reacts selectively with thymidine residues in DNA (1) while hydroxylamine hydrochloride at pH 6 specifically attacks cytosine (2). We have adopted these reactions for use with the chemical sequencing method developed by Maxam and Gilbert (3).     

Construction of a microprocessor-controlled pulsed quench-flow apparatus for the study of fast chemical and biochemical reactions

The construction and operation of a microprocessor-controlled quenched-flow machine are described. Two sets of syringes are moved by high-torque stepping motors to achieve any desired mixing scheme. The dead time of the instrument is pulsed quench-flow operation is of the order of 10 ms. The fastest possible reaction time is 12 ms with the reaction chamber used here; this might be extended downward with other reaction chambers. The reactant volume required is low; 1 ml of solution for each reactant is sufficient for more than 40 kinetic measurements. The machine is tested by alkaline hydrolysis of 2,4-dinitrophenylacetate and used in the investigation of the reaction mechanism of the EcoRI restriction endonuclease and of GTPase activity of ribosomes.     

A new apparatus for studying the effect of hydrostatic pressure on cells in culture

Although mechanical stresses have long been recognized as an important factor in the regulation of bone remodeling, the mechanism underlying this effect has remained obscure. A number of methods have been devised to apply forces to bone tissues and bone-derived cells in order to investigate the biochemical results of mechanical stimuli. In this paper we report a method for applying a well controlled cyclic hydrostatic pressure on cultured ROS 17/2.8 osteoblastic lineage cells. This technique allows the investigation of the true frequency response of cells. Hydrostatic pressure with a 1 Hz frequency decreases alkaline phosphatase activity of confluent osteoblastic-like cells (ROS 17/2.8).