Tracer labeling

The growth rate for tracers labeled with short-Hved isotopes such as P and was about 10—15% per year from 1990 through 1994. This trend reflects the increased use of these radiochemicals for research in molecular biology and genetics I-labeled tracers have also exhibited similar growth rates in this period. On the other hand, the market for C- and H-labeled chemicals essentiaHy leveled off The overaH growth rate for aH tracer chemicals was estimated at 5%/yr for 1990—1994. 

More experimental data where the secondary KIE was larger than the EIE were subsequently published by Subramanian and Saunders (1984). The 2-arylethyl system was employed in these studies because other relevant data, such as the primary deuterium KIE, were available for this reaction. Special techniques were developed to determine the primary and the secondary tritium KIEs for this system. Three isotopically distinct elimination reactions (49-51) are possible for a 2-arylethyl derivative tracer labelled with tritium at the 2-position. 

Yguerabide, J. and Yguerabide, E.E., Light-scattering submicroscopic particles as highly fluorescent analogs and their use as tracer labels in clinical and biological applications. Anal. Biochem., 262, 137-176, 1998. 

The main radiopharmaceuticals labelled with fluorine-18, routinely prepared ([2-i F] fluorodeoxyglucose [ F]FDG [26-28], [i F]fluoro-L-DOPA [29], [i F]altanserin [30, 31], [ F]setoperone [32]) are presented with their uses in Table 2. For comparison, the most common tracers labelled with carbon-11 (methionine [33], palmitic acid [34], flumazenil (RO 15.1788) [35], PK 11195 [36], raclopride [37], deprenyl [38], Way-100635 [39], McN-5652Z [40], CGP 12177 [41]) are shown in Table 3. By far, [ F]FDG is the most widely studied, particularly in oncology for the diagnosis of tumours, detection of sub-clinical diseases, assessment of therapy responses, and detection of recurrence. F-Steroids [42], F-proteins or peptides, or F-labelled tissue specific agents have also been synthesized for the detection and monitoring of various malignancies [43]. 

Figures 1 and 2 compare the uses (oncology vs receptors) of tracers labelled with carbon-11 and with fluorine-18 [44].

It is necessary to provide evidence that these conqtounds are taken up by the plants and that damage to the plants can be directly associated with the presence of these conqtounds in plant tissues or organs. Tracer-labeled phenolic acids can best serve these investigations. Several crucial questions must be answered in order to derive a realistic assessment of plant damage and, furthermore, to devise means to alleviate such damage in the field. For instance, does damage occur at or on the root surface, or is the chemical(s)... 

Methods Tracers/labels Strategy Signal Detection limit References... 

This lipophilic cationic cyanine dye, 339, a tumor specific localizing tracer, labelled with 125I in the 5,5 -positions, has been synthesized324 as outlined in equation 144. 

Results of isotope ratio measurements from an earlier study that used a similar protocol to the one just described are shown in Figure 3. These curves show plasma Isotope levels for both the i.v.oral tracer, labelled as PTA and CTA respectively. It is generally accepted that isotopic enrichment, atom percent excess, of urine reflects that of plasma, and after the initial period of rapid mixing, urinary atom percent excess is used in lieu of plasma measurements. The curves drawn through the data are those generated using the proposed model for calcium kinetics. 

Acridinium ester used as a chemiluminescent tracer. Labeled acridinium ester in the presence of alkaline hydrogen peroxide undergoes chemical changes producing light that is detected at 430 nm by a photomultiplier detector. 

Measuring exponential KIE relationships generally relies upon the use of tracer-labeled isotopically substituted substrates and, consequently, must be done by competitive methods. Two experiments must be performed, one of which measures kn/kT competitively, the other of which measures ko/kj competitively. It is then a simple matter to obtain the exponential relationship for both primary and secondary positions, where ln(kH/kT)H/ln(kD/kT)[) = RS. 

Surface self-diffusion is the two-dimensional analogue of the Brownian motion of molecules in a liquid bulk. Measurements of self-diffusion have to be performed in complete absence of any Marangoni flow caused by surface tension differences. Such experimental conditions are best established in an insoluble monolayer where one part consists of unlabelled and the other of radio-tracer labelled molecules. The movement of molecules within the surface monolayer can be now observed by using a Geiger-Miiller counter. There are possible effects of liquid convective flow in the sublayer which was discussed for example by Vollhardt et al. (1980a). With e special designed apparatus Vollhardt et al. (1980b) studied the self-difihision of different palmitic and stearic acid and stearyl alcohol and obtained self-diffusion coefficients between l-i-4 lO cm /s. 

In 1947, Robert Hofstadter invented the sodium iodide thalhum-activated scintillation crystal, which made possible gamma energy spectrometry, pioneered by P.R.Bell and Craig Harris at ORINS. Spectrometry greatiy improved the efi dency of detection of radioactive tracers labeled with multiple radionuchdes. Crystal detectors were more sensitive in the measurement of radioactivity both in vivo and in vitro. 

Carrier-mediated transport across membranes adds additional complexity to the system and, thus, to the model. For even the simplest transporter, the concentration of the transporter and its affinity for the substrate must be known before it can be modeled. Also, active transport is inherently a saturable process. Thus, to analyze the dynamics of tracer-labeled substrate, the model must account for both labeled and unlabeled substrate as the transport dynamics will depend on total substrate concentration. 

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