Possibilities and pitfalls in quantifying the extent of cysteine sulfenic acid modification of specific proteins within complex biofluids.
BACKGROUND
Cysteine sulfenic acid (Cys-SOH) plays important roles in the redox regulation of numerous proteins. As a relatively unstable posttranslational protein modification it is difficult to quantify the degree to which any particular protein is modified by Cys-SOH within a complex biological environment. The goal of these studies was to move a step beyond detection and into the relative quantification of Cys-SOH within specific proteins found in a complex biological setting--namely, human plasma.


RESULTS
This report describes the possibilities and limitations of performing such analyses based on the use of thionitrobenzoic acid and dimedone-based probes which are commonly employed to trap Cys-SOH. Results obtained by electrospray ionization-based mass spectrometric immunoassay reveal the optimal type of probe for such analyses as well as the reproducible relative quantification of Cys-SOH within albumin and transthyretin extracted from human plasma--the latter as a protein previously unknown to be modified by Cys-SOH.


CONCLUSIONS
The relative quantification of Cys-SOH within specific proteins in a complex biological setting can be accomplished, but several analytical precautions related to trapping, detecting, and quantifying Cys-SOH must be taken into account prior to pursuing its study in such matrices.
Rehder
Douglas S
DS
Molecular Biomarkers, The Biodesign Institute at Arizona State University, Tempe, AZ 85287, USA.
Borges
Chad R
CR
D003512:Cyclohexanones / Q000737:chemistry; D003545:Cysteine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D009579:Nitrobenzoates / Q000737:chemistry; D010084:Oxidation-Reduction; D011228:Prealbumin / Q000737:chemistry*; D012709:Serum Albumin / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013434:Sulfenic Acids / Q000737:chemistry / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000737:chemistry
D003512:Cyclohexanones; D009579:Nitrobenzoates; D011228:Prealbumin; D012709:Serum Albumin; D013434:Sulfenic Acids; D013438:Sulfhydryl Compounds; C011136:thionitrobenzoic acid; C004774:dimedone; C100870:cysteinesulfenic acid; D003545:Cysteine