Low Temperture Research Articles

The influence of protein-lipid interactions on the order-disorder conformational transitions of the hydrocarbon chain

The phases of simple systems involving one type of protein (lysozyme or cytochrome c) and one type of lipid (phosphatidic acid) have been characterized by X-ray crystallography, chemical analysis and spin-labeling technique as a function of temperature. They are of the lamellar type with alternative protein monolayers and lipid bilayers. According to the pH, two types of lamellar phases are obtained, one where the lipid-protein interactions are mainly hydrophobic, the other where they are electrostatic. In both cases, a phase transition occurs as temperature is lowered, between a high temperature phase, where all the lipids are in the liquid-like state, and another phase where some lipid chains are rigid. In the case of the phases with electrostatic interaction, it is shown that the onset of the order-disorder transition is shifted towards low temperature as compared with the homologous lipid-water phase and that the protein content of the phase decreases as the ratio of the liquid to rigid hydrocarbon chains decreases. This leads us to suggest that in the systems studied in this work the proteins interact only with lipid in the liquid-like state. In the case of the phases with hydrophobic interaction, it is shown that the extent of hydrophobic interaction between protein and lipid increases as the unsaturation of the hydrocarbon chains increases. The onset of the order-disorder transition shows a greater shift towards low temperture than the one observed in the case of the phase with electrostatic interaction.

Cyclophanes—VII : Conformations of [2.2](2,5)furanoparacyclophane,[2.2](2,5)furano(1,4)naphthalenophane and [2.2](2,5)furano(9,10)anthracenophane. perpendicularity of aromatic moieties

Variable temperature NMR spectroscopy was used to study the conformational behavior of [2.2](2,5)furanoparacyclophane (1), [2.2](2,5)furano(1,4)naphthalenophane (2) and [2.2](2,5)furano(9,10)anthracenophane (3). While the method was useful in studying 1, it was not adequate for 2 and 3. Variable temperature UV absorption and fluorescence emission studies provided information on the conformations of 2 and 3. The UV absorption and emission spectra of 1 were blue-shifted relative to their ambient temperature spectra. Those of 2 were not shifted at all and those for 3 were red-shifted. The data is consistent with an anti-orientation of the aromatic rings in 2 both at ambient and low temperture. The aromatic rings in 3 are perpendicular to one another at low temperature and probably at room temperature as well. Exiplex bands were absent in the room temperature emission spectra of 1, 2 and 3 as well as the low temperature spectra of 2 and 3. An exciplex band was observed in the low temperature emission spectrum of 1.

Temperature-dependent change in rate-limiting step of the magnesium-stimulated ITPase of myosin.

The effects of temperature on Mg-ITPase activity of heavy meromyosin and myosin subfragment 1 were measured in 0.1 M KC1. The initial burst of Pi liberation was one mol per mol of heavy meromyosin or two mol of myosin subfragment 1, i.e. one mol per two mol of myosin active sites, at 20 degrees C. However, it was almost zero mol below 8degrees C. Effects of KC1 concentration and pH on ITPase activity of heavy meromyosin at 20 degrees C were different from those below 8 degrees C, suggesting that the rate-limiting step in the Mg-ITP hydrolysis of myosin depends on temperature. The effect of temperature on the actin activation of heavy meromyosin Mg-ITPase was analyzed by measuring the temperature dependence of double-reciprocal plots of ITPase activity against actin concentration. The extent of actin activation was larger at low temperture. The results presented in this paper might be explained by assuming the existence of two kinds of active sites on a myosin molecule.

Autoignition of Flowing Hydrogen-Air Mixtures

A shock tube was used to determine the cause of autoignitions occurring at low temperatures in flowing hydrogen-air mixtures. For flow speeds above 750 m/sec, ignitions were observed at temperatures 400K below that established in static mixtures by the thermal explosion limit method. Gasdynamic processes which can produce high local static temperatures were absent. Therefore, the classical concept of does not seem to apply to these spontaneous ignitions. The onset of ignition has been experimentally correlated to the flow speed, the density in the boundary layer, the wall temperature, and the stagnation temperature of the flow. It has been concluded that the low temperature ignition originates in the boundary layer and is caused by friction induced ionization of the hydrogen molecule at the surface of the tube. When the boundary layer is turbulent, the low temperture ignitions do not occur.

Studies on Alkali Decomposition of Rice Kernel : 4) Some alkali tests using "powder method"

Powder method of alkali test on which the author has reported in the previous paper, was applied for an investigation of varietal difference in alkali digestibility of rice flour. Effect of air temperatures on the alkali digestibility was also tested during the ripening periods of rice. Special emphasis was laid upon the comparison of digestibility of milled white rice, rice flour and rice starch. The results were summarized as follows. 1. Alkali decomposition values for rice flours of 108 varieties showed analogus tendency to the values for milled white rice which had been tested previously. All the materials being obtained from the sama source. A highly significant correlation was found between the decomposition values of the two materials, but some difference in regression line was shown between japonica and indica varieties. 2. The values of the powder test were negatively correlated to the mean air temperatures during the ripening periods of 20 day after heading. High temperature treatment (30°C) in the ripening period decreased the decomposition values, whereas low tempertures (23 and 13°C) increased. The effect of temperature was more conspicuous for japonica varieties than for indica ones, indicating higher sensitivity to temperature of the former. 3. Difference in cultural season resulted in different values of alkali decomposition of rice. Late-season-cultured rice showed higher digestibility as compared with early- or mid-season-cultured rice. 4. Alkali digestibility of rice starch which had been separated and refined by alkylbenzen-sulphonate solution was quite analogous to that of rice powder of the same source. 5. The results mentioned above may lead to the conclusion that alkali digestibility of rice is exclusively depending on the digestibility of starch granule. 6. Air temperature which seemed to be the most influential of all the environmental factors in ripening season may cause some changes in micellar structure with in the developing granules of starch, and as a result, a change in swelling character which is connected with alkali digestibility.