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Updated: Aug 15, 2026

Matrix-assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) Mass Spectrometric Analysis of Intact Proteins Larger than 100 kDa
Published on: September 9, 2013
Toward the bilayer proteome, electrospray ionization-mass spectrometry of large, intact transmembrane proteins
J P Whitelegge1, J le Coutre, J C Lee
1Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA. jpw@chem.ucla.edu
Abstract:
Genes encoding membrane proteins comprise a substantial proportion of genomes sequenced to date, but ability to perform structural studies on this portion of the proteome is limited. Electrospray ionization-MS (ESI-MS) of an intact protein generates a profile defining the native covalent state of the gene product and its heterogeneity. Here we apply ESI-MS technology with accuracy exceeding 0.01% to a hydrophobic membrane protein with 12-transmembrane alpha-helices, the full-length lactose permease from Escherichia coli. Furthermore, ESI-MS is used to titrate reactive thiols with N-ethylmaleimide. Treatment of the native protein solubilized in detergent micelles reveals only two reactive thiols, and both are protected by a substrate analog.
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