Labeling methods

Labeling. Radioisotopic labeling, one of the first labeling methods used, is stiU prominent in assays where the use of nonradioisotopic labels... 

The main advantages of plasma-source mass spectrometry (PS-MS) over other analytical techniques, such as PS-AES and ETAAS, are the possibilities of quantitative isotope determination and isotope dilution analysis the rapid spectral scanning capability of the mass spectrometer and semiquantitative determinations to within a factor of two or three. Several labelling methods are used for the quantification of analytes present in complex mixtures. In these methods, the sample is spiked... 

With [32P]phosphoric diimidazolide, prepared from sulfinyldiimidazole or CDI and H332P04, the 5 -terminal monoester phosphate groups in various RNAs could be selectively phosphorylated (radioactive labeling method) 1571,1581... 

The use of the in vivo labeling methods described above is limited by the fact that the sample must be grown in the presence of the labeling isotopes. In many cases, it is not feasible to perform in vivo metabolic labeling. For example, for human clinical samples it is not possible to perform in vivo labeling and yet it is highly desirable to obtain accurate quantitative information on protein expression levels within these samples. Therefore, robust methods are needed for quantitation of protein levels in the absence of in vivo labeling with isotopes. 

The results obtained with the ICAT labeling strategy are similar, in principle, to those obtained by in vivo labeling with stable isotopes in that the relative ratios of proteins from different samples are obtained (Fig. 3.2). The important difference between the methods is that the ICAT-labeling procedure is performed in vitro on protein lysates. Therefore, the ICAT-labeling strategy can be applied to samples that cannot be labeled in vivo. Because the ICAT-labeling method can be used with virtually any sample, it... 

To use the factor-label method, start with the quantity given (not a rate or ratio). Multiply that quantity by a factor, or more than one factor, until an answer with the desired units is obtained. Compare this method with that of Example 2.23(b). 

Since it is a quantitative property, it is often more useful for identification than a qualitative property like color or smell. Moreover, density determines whether an object will float in a given liquid. If the object is less dense than the liquid, it will float if it is more dense, it will sink. It is also useful to discuss density here for practice with the factor-label method of solving problems, and as such, it is often emphasized on early quizzes and examinations. 

In doing numerical density problems, you may always use the equation d = m/V or the same equation rearranged into the forms V = m/d or m = dV. You are often given two of these quantities and asked for the third. You will use the equation d = m/V if you are given mass and volume, but if you are given density and either of the others, you probably should use the factor-label method. That way, you need not manipulate the equation and then substitute you can solve immediately. 

Use of the equation requires manipulation of the basic equation followed by substitution. The factor-label method gives the same result by merely relying on the units. It also allows combination of the solution with other conversions. 

Then the coefficients in the balanced chemical equation can be used as factors in the factor-label method to convert from moles of one chemical to moles of any other in the equation ... 

In the example given in the text above, with 4 mol of nitrogen, it was not necessary to use the factor-label method the numbers were easy enough to work with. However, when the numbers get even slightly complicated, it is useful to use the factor-label method. Note that any of the following factors could be used for this equation, but we used the one above because it is the one that changes moles of hydrogen to moles of ammonia. 

Ans. Section 2.4, factor-label method Sec. 4.4, calculation of formula weights Sec. 4.5. changing moles to grams and vice versa Sec. 4.5, Avogadro s number and/or Sec. 7.2, balancing chemical equations. 

Heat capacities may be used as factors in factor-label method solutions to problems. Be aware that there are two units in the denominator, mass (or moles) and temperature change. Thus, to get energy, one must multiply the heat capacity by both mass (or moles) and temperature change. 

Which of the equations given for AH is used here Both. You can see from the factor-label method solution that the atomic weight divided into the molar heat capacity is the specific heat capacity while the mass divided by atomic weight is the number of moles. Thus, we have cither moles times molar heat capacity times change in temperature or mass times specific heat times change in temperature. 

Yano Y, Matsuzaki K (2009) Tag-probe labeling methods for live-cell imaging of membrane proteins. Biochim Biophys Acta-Biomembranes 1788 2124—2131... 

Manduchi, E., Scearce, M., Brestelli, J.E., Grant, G.R., Kaestner, K.H., and Stoeckert, C.J. (2002) Comparison of different labeling methods for two-channel high-density microarray experiments. Physiol. Genom. 10, 169-179. 

---