The described approach to protein quantitation, based on the use of an exogenous IRS that is co-extracted by a multiplexed antibody system, has been previously discussed [22], [23], however, this is the first report of such an approach in the quantitative measurement of RBP4.
The label-free quantitation based on peptide-spectral counts offers a high-coverage identification of proteins, and then gives a comprehensive and rapid comparison to the differential proteins, especially to the plasma proteins [48].
An advantage of this labeling approach is the stoichiometric attachment of one label per glycan, allowing a direct quantitation based on fluorescence or UV-absorbance intensity.
Though mass spectrometric analyses of this type are not fully quantitative, recent studies have established that relative quantitation based on the signal strength of permethylated glycans analyzed by MALDI-TOF MS is indeed both possible and accurate, especially when comparisons are carried out among related species across small mass ranges (Wada et al. 2007).
The exploration of spectral counting quantitation based on LC-MS presented here gathers experimental evidence of the influence of batch effects on comparative proteomics.
For each mouse brain the spectrum of the relative amount of metabolites inside the experimental PRESS volume was quantified using the QUEST (quantitation based on quantum estimation) module [124] available inside the Java Magnetic Resonance User Interface (JMRUI) package [125].
An algorithm was constructed to assess the self-consistency of the quantitation based on known relationships between the elutriated fractions.
Label-free quantitation was performed using MS1 peak area as described previously, and total protein quantitation based on MS2 spectral counting was performed via ProteoIQ label-free quantitation software (NuSep, Bogart, GA, USA).
While this method includes lung segmentation of both the parenchyma and central vasculature, these vessels are ultimately excluded in quantitation based on the attenuation values of blood (~40 HUs depending on the hematocrit).
Quantitation was based on a gallic acid standard calibration curve.
