REACTIVE SPECIES - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 13

TABLE 1.3. Primary Products and Corresponding Mass Changes for Various Amino
Acid Side Chains Subjected to Radiolytic Modification and Detectible by Mass
Spectrometry
Side Chain Side-Chain Modification and Mass Changes

Cys Sulfonic acid (+48), sulfinic acid (+32), hydroxy (−16)

Cystine Sulfonic acid, sulfinic acid

Met Sulfoxide (+16), sulfone (+32), aldehyde (−32)

Trp Hydroxy- (+16, +32, +48, etc.), pyrrol ring-open (+32, etc.)

Tyr Hydroxy- (+16, +32, etc.)

Phe

Hydroxy- (+16, +32, etc.)

His Oxo- (+16), ring-open (−22, −10, +5)

Leu a Hydroxy- (+16), carbonyl (+14)

Ile a Hydroxy- (+16), carbonyl (+14)

Val a Hydroxy- (+16), carbonyl (+14)

Pro Hydroxy- (+16), carbonyl (+14)

Arg Deguanidination (−43), hydroxy- (+16), carbonyl (+14)

Lys

Hydroxy- (+16), carbonyl (+14)

Glu Decarboxylation (−30), hydroxy- (+16), carbonyl (+14)

Gln Hydroxy- (+16), carbonyl (+14)

Asp Decarboxylation (−30), hydroxy- (+16)

Asn Hydroxy- (+16)

Scr b Hydroxy- (+16), carbonyl (−2-or +16-H 2 O)

Thr b Hydroxy- (+16), carbonyl (−2-or +16-H 2 O)

Ala Hydroxy- (+16)

a For aliphatic side chains, +14 Da products are normally much less than +16 Da products.
b For Ser and Thr, only trivial amounts of +16 and −2 Da products were found.
Adapted from Xu and Chance [87] with the permission of the American Chemical Society.

137, 144]. Different oxidation products detected in model proteins, ubiquitin
and apomyoglobin, using a nanosecond laser-induced photochemical oxida-
tion method are presented in Table 1.4 and Table 1.5 [141]. A single shot of
the laser resulted in 70% and 90% oxidation of ubiquitin and apomyoglobin,
respectively, and different surface amino acids residues were oxidized. The
liquid chromatography (LC)/MS/MS analysis of trypsin-digested apomyoglo-
bin showed 99.3% sequence coverage. Extensive protein surface modifications
of ubiquitin and β-lactoglobulin were seen in one submicrosecond electron
beam pulse [142]. Fast photochemical oxidation of protein (FPOP) utilizing
• OH radicals has also been used to characterize the epitope of the serine
protease thrombin [145].

1.2.2 Other Techniques

In the last two decades, the approach of side-chain modification coupled
with proteolysis and MS has been applied extensively to analyze protein