Tritiated water release

Figure 3 Dowex AB 1-X8 borate resin micro-column estimation of tritiated water released from 1 mM...

In a yeast estrogen screen assay, damiana exhibited estrogenic activity. In a tritiated-water release assay, a methanol extract of damiana dose-dependently inhibited aromatase (Zhao et al. 2008). 

The radiological hazard of tritium to operating personnel and the general population is controlled by limiting the rates of exposure and release of material. Maximum permissible concentrations (MPC) of radionucHdes were specified in 1959 by the International Commission on Radiological Protection (79). For purposes of control all tritium is assumed to be tritiated water, the most readily assimilated form. The MPC of tritium ia breathing air (continuous exposure for 40 h/wk) is specified as 185 kBq/mL (5 p.Ci/mL) and the MPC for tritium in drinking water is set at 3.7 GBq/mL (0.1 Ci/mL) (79). The maximum permitted body burden is 37 MBq (one millicurie). Whenever bioassay indicates this value has been exceeded, the individual is withdrawn from further work with tritium until the level of tritium is reduced. 

Direct Methods. The classical approach has been to prepare tritiated or carbon labeled analogs of the parent hydrocarbons which may then be used in animal or in vitro experiments. Tritiated compounds are generally easier to prepare, using exchange reactions on the parent hydrocarbon, than their 14C analogs and have higher specific activities. However, during the metabolism of such compounds, some of the tritium is released as tritiated water, either directly or... 

Figure 6. Time course of tritiated water uptake or release from bean leaf discs previously exposed to 0.5 ppm ozone for 1 hr immediately prior to experiment. Upper Discs were preincubated in 0.2 M mannitol for 2 hr then transferred to tritiated water. Lower Discs were preincubated in tritiated water then transferred to 0.2 M mannitol. Data of Evans and Ting (13).

Both mechanisms seem to be consistent with incorporation of a label from tritiated water into 101 (at C-2),412 but not into the unreacted glycosyl pyrophosphate esters,413 and also with kinetic evidence414 for liberation of the pyrophosphate 6 prior to release of 101. No requirement for added NAD has been reported, and a search for pyridine nucleotide firmly bound to the enzyme may lead to conclusive evidence for the mechanism. 

The present work was undertaken in an attempt to shed light on the mechanism of hydroxyproline formation in collagen biosynthesis and on the site of action of ascorbate. It was recognized that these phenomena were very likely to be closely interrelated. Proline labeled with tritium was used because it was anticipated that tritium released from proline during hydroxylation would appear in the tissue water as tritiated water. The use of tritiated proline in such a system might then provide a new parameter for following the hydroxylation reaction, provided that the formation of tritiated water was stoichiometrically related to the formation of hydroxyproline. Such an approach might conceivably permit the demonstration of hydroxylation and peptide bond formation as separate chemical steps. 

It is evident that the studies with tritiated proline do not permit definite conclusions about the mechanism of hydroxylation further information is needed about the labeling of the proline used and possible isotope effects. It is probable that there is some randomization of label during tritiation of 3,4-dehydroproline (40), and apparently also some racemization. Thus, we have observed that the tritiated proline preparations contain 10 to 20% D-proline and that oxidation by D-amino acid oxidase releases significant amounts of tritiated water. 

Tritium, however, was largely released directly to the stratosphere, where it is oxidized to tritiated water vapor. It is subseqently mixed back into the troposphere, predominantly at mid-latimdes and rapidly rained out as tritiated rainfall (e.g., see Weiss and Roether, 1980). Thus, there is a far greater asymmetry between the two hemispheres, and characteristically different deposition histories. Figure 7 shows the hrst two EOFs of the tritium in precipitation as analyzed by Doney (Doney et ai, 1992) from IAEA data. The pattern decomposes into two dominant factors a northern impulse (the largest component) and a smaller, more diffuse southern component. 

The equilibrium constant for the TIM-catalyzed reaction is 22 in the direction of DHAP for the reactive, nonhydrated forms of DHAP and G3P [8] as a result, steady-state kinetics as well as the fates of substrate- and solvent-derived protons can be studied using either DHAP or G3P as substrate. In a series of landmark papers, Knowles and Albery quantitated the free energy profile for the reaction (Fig. 6.1) [37-42]. These studies utilized protiated, deuteriated, and tritiated forms of both DHAP and G3P in both unlabeled and tritiated water to follow the course of the transferred proton(s) during the course of the reaction. Several important conclusions were reached (i) for protiated substrates, the transition state for binding/release of G3P is the highest point on the energy diagram (ii) for tritiated... 

Basically three options are considered to dispose of tritiated water that is stored in tanks and cannot be released. 

Collection and analysis complexity introduced by forms other than tritiated water is discussed in Section 6.2.2. Tritium is released in these forms from nuclear facilities or converted to them in the environment. These forms generally occur in lesser magnitude than tritiated water they should be differentiated because of their different pathways and radiation impacts after they enter the body. Biological material can be dried to collect tritium as water vapor and then ashed to collect organic tritium as HTO vapor. 

The investigators foimd that both the thermal and enzyme-catalyzed reactions of (E)-[9- H jchorismate led to rapid release of tritiated water, whereas the reactions of the (Z) isomer did not. From this they concluded that both the enzyme-catalyzed and thermal reactions involve a chair-like transition structure. 

The T released from neutron-irradiated borosilicate glass was determined by using a specially designed sampling system and a liquid scintillation counter at 200 to 700C. It was found that the chemical form of T released was mainly tritiated water (HTO, T2O). The T produced in the glass tended to react with O to form OT and to diffuse... 

Cleanup systems such as filters and ion exchange columns should be used to remove contaminants from reactor coolant. These can become significant sources of radiation, however. For reactors moderated or cooled by heavy water, the release of such material would also generate a hazard from the inhalation or absorption of tritiated water in vapour form. 

These two methods produce different release profiles in vitro. Figure 5 demonstrates the release kinetics of BCNU from wafers loaded with 2.5% BCNU pressed from materials produced using these two methods. The wafers containing tritiated BCNU were placed into beakers containing 200-ml aliquots of 0.1 M phosphate buffer, pH 7.4, which were placed in a shaking water bath maintained at 37 C. The shaking rate was 20 cycles/min to avoid mechanical disruption of the wafers. The supernatant fluid was sampled periodically, and the BCNU released was determined by liquid scintillation spectrometry. The BCNU was completely released from the wafers prepared by the trituration method within the first 72 hr, whereas it took just about twice as long for the BCNU to be released from wafers... 

To begin the experiment, each female (18—25 g) was removed, injected with tritiated PGp2 (Dupont NEN, Boston, MA 3.6 pCi or -3,600,000 cpm, 20 pg PGF2 ), briefly dipped into another bucket of water to rinse off excess radiation, and returned to the experimental apparatus. The pump withdrew water at 5 ml/10 s, and 5 ml samples were collected every minute from 15-45 min after returning the female to the apparatus. We chose 1 min intervals because it was the fastest rate at which we could sample reliably and because Experiment 1 demonstrated that goldfish typically urinate less than once per minute. Water samples were mixed with scintillation fluid in a 1 3 ratio, and radiation levels of samples were measured in a scintillation counter. Each sample was counted three times, and the average for each sample was used to calculate (see below) whether or not an increase in radiation was attributable to urinary release. 

Protoberberines were reduced with NaB H4. The tritiated (S)-tetrahydroproto-berberines were methylated by the (S)-tetrahydroprotoberberine-cis-N-methyl-transferase. If the (S)-cis-N-methyltetrahydroprotoberberines are hydroxyl-ated a H-release into water can be measured. 

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