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Easy numbers

User: Catherine Fenselau, professor of chemistry and biochemistry, University of Maryland, College Park Related Articles Peak Addition Tips for Quantifying Mass Spec Clean targeting Multiplex counts Label-free Metabolic power Project: Identifying molecular mechanisms of drug resistance in breast cancer Problem: Fenselau works with several drug-resistant and drug-sensitive cell lines, and she wanted a cheap and simple

Jeffrey M. Perkel

User:
Catherine Fenselau, professor of chemistry and biochemistry, University of Maryland, College Park

Project:
Identifying molecular mechanisms of drug resistance in breast cancer

Problem:
Fenselau works with several drug-resistant and drug-sensitive cell lines, and she wanted a cheap and simple way to compare protein abundance among them.

Solution:
Fenselau's approach, proteolytic 18O labeling, is simplicity itself. "It works, we know how to do it, and it's less expensive than other methods, especially metabolic labeling," she says. Two protein extracts are digested to peptides, one in normal 16O water, and the other in labeled 18O water. Each peptide produces two peaks differing in mass by 4 Daltons (because two water molecules are used in the cleavage reaction); the ratio of peaks reveals how the peptide's abundance in one sample compares with the...

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