Folded and unfolded

Proteins in their native state, tend to produce multiply charged ions covering a smaller range of charge states. These charge states tend to have fewer charges than an unfolded protein would have, due to the inaccessibility of

many of the protonation sites.

Increasing the sampling cone voltage may provide sufficient energy for the protein to begin to unfold and create

a wider charge state distribution centering on more highly charged ions in the lower m/z region of the spectrum.

Folded and unfolded statesHolo and apo proteins

30-Oct-199814:50:44apo-pseudoazurin + Cu BMB, The University of Leeds

600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000m/z0

100

%

0

100

%

SJ06 1 (1.242) Sm (SG, 2x1.00); Sb (10,10.00 ) Scan ES+ 9.15e5A9;1494.9

A101345.5

1223.7

1490.7

B81693.9

B91506.0

1513.01676.8

1706.5B7

1935.81718.6

SJ04 1 (1.415) Sm (SG, 2x1.00); Sb (10,10.00 ) Scan ES+ 2.08e6A15;893.0

A17788.0

744.5

A19705.3

A14956.7

A131030.3

958.5

A121116.0

1034.9

A111217.3 A10

1339.0 A91487.8

MW 13,381 Da apo-pseudoazurinanalysed in 1:1 aq. MeCN, pH 2

MW 13,444 Daapo-pseudoazurin with Cu bound analysed in water, pH 7

Positive or Negative Ionisation? 

 If the sample has functional groups that readily accept a proton (H+) then positive ion detection is used

e.g. amines R-NH2 + H+ R-NH3+

as in proteins, peptides

 If the sample has functional groups that readily lose a proton then negative ion detection is used e.g. carboxylic acids R-CO2H R-CO2

– and alcohols R-OH R-O– as

in saccharides, oligonucleotides

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Training and education

WEB

Articles

Vestling, M.M.USING MASS SPECTROMETRY FOR PROTEINSJ. Chem. Ed. 2003, 80, 122

AtmosphericPressure

Chemical Ionization

zV

1/2mv2=cost