Objective Ischaemia-modified albumin (IMA) has been demonstrated to be a biomarker of ischaemia associated with myocardial and skeletal muscle ischaemia, pulmonary embolism and stroke. However there is limited information on the formation mechanism of IMA. The aim of the study was to investigate the primary and secondary protein structure of IMA.

Methods This study included 29 acute coronary patients (IMA level>0.8 absorbance units) and 22 healthy controls (IMA level <0.5 absorbance units). Serum IMA was purified by salting out and ion exchange chromatography. We also chose 21 human albumin standard. The structures of purified protein and albumin standard were analysed by mass spectrometry, N-terminal sequencings and circular dichroism (CD) spectra measurement.

Results Protein sequences showed that the first 10 N-terminal amino acid residues of IMA were identical with those of albumin in healthy persons. The result of CD spectra measurement revealed that the average percentages of α-helixes and random coil decreased and the average percentages of β-turn and β pleated sheets increased a bit in ACS patients, but there is no significant difference between groups.

Conclusion Compared with the normal human albumin, no changes take place in the N-terminal protein sequence of IMA, and the secondary structure of IMA was also not significantly changed. Increasing percentage of β-turn and β pleated sheets in IMA may correlate with its formation mechanism.