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Isotopic Labeling With Carbon-14 and Tritium
Published in Lelio G. Colombetti, Principles of Radiopharmacology, 2019
In isotopic labeling, a compound is labeled with an isotope of an element already present in the compound so that it is identical (apart from the isotope) with the normal unlabeled form. It should be clearly distinguished from nonisotopic, sometimes referred to as nonnuclidic, labeling in which a compound is labeled with an isotope of a “foreign” element not normally present in the unlabeled substance. Examples of the latter type are the numerous peptides and proteins labeled with radioactive iodine isotopes.
Radioactivity and Radiotracers
Published in Graham Lappin, Simon Temple, Radiotracers in Drug Development, 2006
The other method of introducing a radiotracer into a compound is by addition to the molecule. In this case, unlike substitution, the compound is structurally altered. A common example is where therapeutic proteins are under study (1.4). Proteins are obtained from biological sources and since they are not chemically synthesized, substituting a stable isotope with a radioisotope other than 3H is very difficult. The alternative is therefore to iodinate the protein with 125I, or sometimes with 131I, although a range of isotopes have been used from Bromine to Samarium.3 It may be necessary under such circumstances to demonstrate that the iodinated protein is an adequate surrogate for the intended therapeutic product. This is typically undertaken with a protein-receptor binding assay. Historically this method is known as non-isotopic labeling. The terms isotopic and non-isotopic labeling have however, become less common in recent years. Indeed the terminology has become confused as non-isotopic labeling is sometimes used for fluorescent labels, or other methods where isotopes are not relevant.
Dictionary
Published in Mario P. Iturralde, Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990
Isotopic labeling. It refers to a compound in which an atom has been replaced by an isotope of the same element, in the same position, and without any other change in the molecule; it also refers to compounds in which more than one atom has been replaced under the same conditions.
Advances in phosphoproteomics and its application to COPD
Published in Expert Review of Proteomics, 2022
Xiaoyin Zeng, Yanting Lan, Jing Xiao, Longbo Hu, Long Tan, Mengdi Liang, Xufei Wang, Shaohua Lu, Tao Peng, Fei Long
Stable isotope labeling using amino acids (SILAC) is a metabolic labeling method that involves binding isotopes to samples for cell culture, relative quantification by comparing isotope peak shape area size in primary mass spectra, and identifying peptides in secondary mass spectrometry maps. Zanivan et al. [97] used the SILAC technique in a mouse model to study phosphorylated proteins during skin cancer development. Stepath et al. [98] compared SILAC, TMT, and label-free quantification of phosphorylation sites in the epidermal growth factor receptor (EGFR) signaling pathway in colorectal cancer. They found that SILAC was more accurate than TMT and nonlabeled quantification for the quantification of phosphorylation sites. In addition to SILAC, ICAT and 18O isotope labeling were also quantified based on primary spectrograms. Isotope-coded affinity tag (ICAT) is a chemical labeling method, and ICAT is a chemical reagent labeled with an isotopically encoded chemical reagent on specific amino acid residues of a peptide segment chemical reaction for quantification [99]. In contrast, 18O isotope labeling belongs to enzymatic reaction labeling, quantified by adding 18O isotope labels to the enzymatic reaction [100]. However, these two methods are not widely used at present.
Use of proteomics to detect sex-related differences in effects of toxicants: implications for using proteomics in toxicology
Published in Critical Reviews in Toxicology, 2018
Ivonne M. C. M. Rietjens, Jacques Vervoort, Anna Maslowska-Górnicz, Nico Van den Brink, Karsten Beekmann
Table 1 reveals that several approaches have been used to measure differences in protein abundance upon exposure to toxicants. In a number of studies 2D-differential Gel Electrophoresis (2-DIGE or 2-DE) has been applied to the protein mixtures. This 2-DIGE/2-DE technique separates the proteins based on molecular charge in the first dimension (using isoelectro focusing methods) and based on mass in the second dimension using SDS-PAGE principles (Chandramouli and Qian 2009). The 2-DE method for protein identification is a useful method as differences in abundant proteins can be visualized and using specific software tools differences in protein spots can be observed with subsequent identification of the spots using either MALDI-TOF (or MALDI-TOF/TOF) or LC-ESI-MS/MS. It is important to stress that quantification from optical density measurements has to be handled with care because spots or peaks in LC chromatograms may contain more than one protein, hence the optical density or peak intensity may represent a mixture of proteins (Thiede et al. 2013). A solution to this problem is to apply isotopic labeling (Thiede et al. 2013). Then relative quantification can be performed by MS directly with peptides of the interesting protein species and protein species abundance ratios can be determined between different biological situations.
Dietary vitamin K is remodeled by gut microbiota and influences community composition
Published in Gut Microbes, 2021
Jessie L. Ellis, J. Philip Karl, Angela M. Oliverio, Xueyan Fu, Jason W. Soares, Benjamin E. Wolfe, Christopher J. Hernandez, Joel B. Mason, Sarah L. Booth
In Study 2 (in which all diets were vitamin K sufficient), the cecal microbial community composition at sacrifice was significantly different by sex (PERMANOVA r2 = 0.38 and P < .001, Supplemental Figure 3a), but did not differ by diet in either female or male mice (Supplemental Figure 3b and 3c). No differences were observed in composition between unlabeled (control) and stable-isotope labeled diets that would suggest an influence of the stable isotope labeling, though this cannot be entirely ruled out. Shannon diversity was again significantly greater in female mice as compared to males (r2 = 0.49, P < .001), but did not statistically differ by diet group (data not shown).