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Heterogeneity in human cardiac troponin I standards
D M Bunk1, J J Dalluge, M J Welch
1Chemical Science and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8392, Gaithersburg, Maryland 20899, USA. david.bunk@nist.gov
Abstract:
The LC-MS analysis of recombinant cardiac troponin I (cTnI) and cTnI extracted from human hearts showed a high degree of structural heterogeneity among all samples. The examined recombinant cTnI samples indicated posttranslational modifications, presumably due to their purification (i.e., 2-mercaptoethanol adducts and carbamylation) and related to their expression (i.e., an N-terminal expression tag). The extracted cTnI samples, while having a higher degree of structural heterogeneity, showed less structural variance between samples than the recombinant proteins. The LC-MS analysis of the extracted cTnI samples provided evidence of posttranslational modification by phosphorylation, acetylation, proteolytic cleavage, and intrachain disulfide bond formation.