The water proton spin-lattice relaxation times in virus-infected cells.

The water proton spin-lattice relaxation times in HEp-2 cell cultures were determined immediately after 1 h of polio-virus adsorption. The shortening of the water T1 was closely related to the multiplicity of infection, allowing direct inspections of the virus--cell interaction since the first steps of the infectious cycle. Virus-induced structural and conformational changes of cell constituents were suggested to be detectable by NMR investigation of cell water.     

Viscosity of water in hibernating and nonhibernating mammals estimated by proton NMR relaxation times.

Longitudinal (T1) and transverse (T2) nuclear magnetic resonance relaxation times were measured in vitro at 37, 30, 25, 15, and 5 degrees C on serum, brain, liver, kidney, and heart samples from a hibernator, the European hamster, active in summer (SA), active in winter, or in the hibernating state in winter; from a less efficient hibernator, the golden hamster; and from a homeotherm, the rat. T1 and T2 relaxation times varied between species and in the European hamster between the active and hibernating subjects. Despite the major relaxation time differences between the organs, NMR relaxation time measurements showed a general trend to an increase in the viscosity of water for the European hamster in the active state. Although these modifications were not directly related to the process of hibernation itself, the relaxation times observed in the hibernating animals were closer to those seen in the rat. This evidenced that changes of physical properties of water reflect a better adaptation to low temperatures of the hamster, as compared to the nonhibernator, given that the low water viscosity of SA hamster allows the decrease of the viscosity with temperature during the hibernating state. These in vitro studies permit the study the viscosity which is an important physicochemical parameter involved in NMR longitudinal relaxation time of water proton. More detailed studies of other physiological parameters must be undertaken by further in vivo measurements.     

Frequency dependence of water proton longitudinal NMR relaxation times in mouse tissues around the freezing transition

Water proton longitudinal NMR relaxation times were measured in various tissues of healthy and tumor-bearing mice. Measurements were performed as a function of the Larmor frequency nu in the range 6-90 MHz, and at two temperatures (theta + and theta -) bracketing the 'freezing transition', at which the major part of the water signal disappears. At both temperatures, 1/T1 behaves according to: 1/T1 = A/square root nu + B A and B are obtained at theta + and theta -, and yield the proportion of bound water, which is convincingly identified with non-freezable water. The proportions found lie around 6% for tumors and 12% for other tissues. Discrimination between tissues via T1 is demonstrated to be essentially due to the bound water proportion. Bound water on the one hand and free water on the other hand behave similarly in all tissues including tumors. The activation energy for free water is found to be identical to that of pure water, although relaxation times are markedly different. It is noticed that determining the bound water proportion by signal intensity measurements at theta + and theta - is less reliable than by the T1 method.     

Influence of transition metal ions on NMR proton T1 relaxation times of serum, blood, and red cells

The spin-lattice relaxation rates (1/T1) of serum, whole blood, and red cells were measured vs several concentrations of transition metal ions. For comparative purposes, the similar experiments were repeated in water. The rates show a linear dependence on concentration of each ion for water, but nearly a linear dependence for blood and its constituents. The influence of each ion on 1/T1 in a sample was expressed by the slope (relaxivity) of the least-squares fitting of 1/T1 vs ion concentration. The relaxivities of Mn(II) in serum and of Fe(III) in serum and blood are greater than those in water, whereas the relaxivities of these ions in the other cases and of all the other ions in call cases are smaller than those in water. However, the relaxivity data show that Cr(III) in serum and blood affects the 1/T1 rates. The ratio of relaxivity of each sample to that of water is known as proton relaxation enhancement (PRR) factor (epsilon). The epsilon factors for present data suggest that the added ions are bound to proteins, and only Mn(II) in serum and Fe(III) in blood and serum are accessible to water.     

The comparative influence of anesthetics on the in vitro proton NMR relaxation times in rat liver

To determine the effect of anesthetics on liver relaxation times in rat, two experiments were performed. In the first experiment, normal and protein-depleted rats underwent total hepatectomy under ether anesthesia or following decapitation. In the second experiment, livers were excised from normal rats under ketamine or pentobarbital anesthesia, or following decapitation. Hepatic T1 and T2 were measured for all animals using a RADX 10 MHz spin analyzer. Ketamine produced T1 values significantly different from decapitation. Ketamine, pentobarbital, and ether in normal animals all produced T2 values significantly different from decapitation. It is apparent that anesthetization of rats prior to in vitro measurement of hepatic relaxation times is not equivalent to decapitation; nor are the anesthetics examined equivalent to one another.     

NMR relaxation times of water protons in human colon cancer cell lines and clones

Established lines of human colon cancer cells from several sources (LS180, LS174T, HT29, SW480, SW1345) had water proton nuclear magnetic resonance (NMR) spin-lattice relaxation times (T1) of 460 +/- 45 msec to 982 +/- 9 msec and spin-spin relaxation times (T2) of 83 +/- 6 msec to 176 +/- 6 msec. Two clones derived from single cells of line LS174T were similar in T1 and T2 to the parent line. Differences among the cell lines were not totally a function of cellular hydration. Normal adult and fetal human primary colon cells were wetter and had higher T1 and T2 values than established cell lines. Relaxation times in this study substantiate variations seen for human colon tumors in earlier studies. Established cell lines maintained water relaxation times similar to tumor tissue values. Along with other morphological and biochemical criteria, the relaxation times suggest that these established human colon cancer cell lines may serve as a good experimental model for the study of human colon cancer.     

Relationships between nuclear DNA content and seed and leaf size in soybean

 A correlation between genome size and agronomically important traits has been observed in many plant species. The goal of the present research was to determine the relationship between genome size, seed size, and leaf width and length in soybean [Glycine max (L.) Merr.] Twelve soybean strains, representing three distinct seed size groups, were analyzed. Flow cytometry was used to estimate their 2C nuclear DNA contents. Data on seed size and leaf size of the 12 strains were obtained from 1994 and 1995 field experiments. Variation of 2C nuclear DNA among the 12 soybean strains was 4.6%, ranging from 2.37 pg for a small-seed strain to 2.48 pg for a large-seed strain. Strain seed size was positively associated with leaf width (r=0.92) and leaf length (r=0.93). Genome size was highly correlated with seed size (r=0.97), leaf width (r=0.90) , and leaf length (r=0.93). The results of our study indicate that there is a significant correlation between genome size and leaf and seed size in soybean. It is possible that selection for greater seed size either leads to, or results from, greater genome size. If so, this relationship might be worth exploring at a more fundamental level. Received: 5 April 1997 / Accepted: 9 January 1998     

Mobility of water bound to biological membranes: A proton NMR relaxation study

Water proton nuclear magnetic resonance relaxation measurements have been obtained for aqueous suspensions of red cell membranes. These data support a model in which water molecules are exchanging rapidly between a bound phase with restricted motions and a free phase with dynamic properties similar to liquid water. From this model and these data, estimates are obtained for the relaxation time for bound phase water. Possible relaxation mechanisms for bound phase water are discussed and some support is found for an intermolecular interaction modulated by translational motions characterized by a diffusion constant of 10^?9 cm²/s.     

Sodium-23 NMR relaxation times in nucleated red blood cells and suspensions of nuclei.

The relaxation behavior of intracellular 23Na in suspensions of chicken erythrocytes and of their nuclei was investigated. The transverse magnetization was found to decay biexponentially. The average relaxation rates for the nucleated chicken erythrocytes are considerably shorter than the average relaxation rates obtained for dog and human nonnucleated red blood cells. Of particular significance is the twofold decrease in the short component of T2. Calculations based on the measured 23Na NMR relaxation rates in suspensions of nuclei indicate that most of the difference between the relaxation rates in the mammalian as compared to the chicken erythrocytes, can be accounted for by the contribution of the nuclei in the latter.     

Post mortem changes in skeletal muscle proton spin-lattice relaxation times

A previously published report indicated that there are early post mortem changes in the pulsed NMR proton spin-lattice relaxation time (T1) of skeletal muscle which must be taken into account in in vitro tissue analysis. We re-examined this subject. When T1 measurements were done by allowing the signal intensity to decay over two orders of magnitude from the original intensity, the T1 decay curves showed more than a single exponential relaxation time component as reported earlier. However, when T1 measurements were done by allowing signal intensity to decay to about one order of magnitude from the original intensity only a single exponential relaxation time component was found. We postulate that the latter method gives the average T1 value of the various macroscopic tissue components present and that this method gives a representative T1 value for the entire tissue. Using data obtained in this manner we could not find significant post mortem changes in the muscle T1 relaxation times during the first four hours but found change at a later time.     

土壤含水量与N2O产生途径研究

土壤含水量变化对Ｎ２Ｏ产生和排放影响的研究表明,不同含水量情况下,Ｎ２Ｏ排放也不相同．特别是用乙炔抑制技术证明了在播种前后,气候干燥而土壤含水量较低的情况下,Ｎ２Ｏ产生主要来自于硝化过程;降雨后,土壤含水量较高时,Ｎ２Ｏ主要是通过反硝化过程产生;而在农田中等含水量情况下,土壤微生物的硝化和反硝化作用产生的Ｎ２Ｏ大约各占一半．指出旱作农田Ｎ２Ｏ产生途径主要取决于土壤水分的控制和调节．     

Mobility of water bound to biological membranes. A proton NMR relaxation study.

Water proton nuclear magnetic resonance relaxation measurements have been obtained for aqueous suspensions of red cell membranes. These data support a model in which water molecules are exchanging rapidly between a bound phase with restricted motions and a free phase with dynamic properties similar to liquid water. From this model and these data, estimates are obtained for the relaxation time for bound phase water. Possible relaxation mechanisms for bound phase water are discussed and some support is found for an intermolecular interaction modulated by translational motions characterized by a diffusion constant of 10(-9) cm2/s.     

Hexagonal ice in pure water and biological NMR samples

Ice, in addition to “liquid” water and protein, is an important component of protein samples for NMR spectroscopy at subfreezing temperatures but it has rarely been observed spectroscopically in this context. We characterize its spectroscopic behavior in the temperature range from 100 to 273 K, and find that it behaves like pure water ice. The interference of magic-angle spinning (MAS) as well as rf multiple-pulse sequences with Bjerrum-defect motion greatly influences the ice spectra.     

Evaluation of the water environments in deoxygenated sickle cells by longitudinal and transverse water proton relaxation rates

The longitudinal and transverse water proton relaxation rates of oxygenated and deoxygenated erythrocytes from both normal adults and individuals with sickle cell disease were measured as a function of temperature at two different frequencies. The simplest model which fits all of the data consists of three different environments for water molecules. The majority of the water (98%) has a correlation time indistinguishable from bulk water (3 × 10^?11 sec). Secondly, there is a small amount of water (1.3–1.5%) present which has a correlation time of 2–4 × 10 ^?9 sec and is apparently independent of the erythrocyte sample studied. Presumably this water is the hydration sphere around the hemoglobin molecules and its correlation time is significantly slower than bulk water. The third environment contains approximately 0.2% of the water present and has a correlation time≥ 10^?7 sec. This third environment is considered tightly bound to the hemoglobin because the water proton correlation time is very similar to the expected rotational correlation time for the hemoglobin molecules. The value of the transverse relaxation rate, f_b(T_2b)^?1, for the tightly bound water fraction decreases in oxy ($\text{S}\text{S}$), deoxy ($\text{A}\text{A}$), and oxy ($\text{A}\text{A}$) erythrocyte samples as the temperature is increased as expected for a rotational correlation time process. In dramatic contrast,f_b (T_2b)^?1 increases almost linearly as the temperature is increased over the whole 4 ° to 37 °C temperature range in samples of deoxy ($\text{S}\text{S}$) erythrocytes. The observation suggests a continual increase in the formation of deoxyhemoglobulin S polymers rather than a sudden transition from a homogeneous solution of deoxyhemoglobin S molecules to a solid gel.