Abstract:
Changes in the amide bands in Fourier Transform Infrared (FTIR) spectrometry are attributed to alterations in the secondary structures of proteins. The interaction of antimalarial drugs (pyrimethamine and sulphadoxine) with HbA, HbAS and HbS at different pH values; ( pH 5.0 and pH 7.2) have been studied by FTIR spectrometry in the mid- infrared region, 4000 – 200cm-1. While pH 5.0 is the pH of the digestive food vacuole of the malarial parasite, pH 7.2 is the physiological pH of the human body. In this study, the spectra of haemoglobin A, AS and S at pH 5.0 and pH 7.2 were analysed. At pH 5.0, HbA exhibited absorption spectra at the regions of 1688.52cm-1 and 1625cm-1 which according to literature, signified beta sheet and beta turn contents. When the protein was mixed with the drugs(pyrimethamine and sulphadoxine), it exhibited an absorption spectrum at the region of 1658.36cm-1 which signified alpha helix contents. At the same pH of 5.0, HbAS exhibited an absorption spectrum at the region of 1656.84cm-1 signifying alpha helix and when combined with the drugs, exhibited an absorption spectrum at the region of 1644cm-1 which signified beta sheet contents. At pH 5.0 also, HbS exhibited an absorption spectrum at the region of 1654.92cm-1 signifying alpha helix and when mixed with the drugs in combination, exhibited absorption spectra at regions of 1688.52cm-1 and 1626.12cm-1 which signified beta sheet and beta turn contents. At pH 7.2, HbA exhibited an absorption spectrum at the region of 1622.28cm-1 signifying beta sheetand when mixed with the drugs, showed an absorption spectrum at the region of 1623.24cm-1 which also signified beta sheet contents. HbAS at pH 7.2 exhibited an absorption spectrum at the region of 1657.80cm-1 signifying the presence of alpha helix and when combined with the drugs, exhibited an absorption spectrum at the region of 1663.56cm-1 which signified 3-10 helix contents. At the same pH of 7.2, HbS exhibited an absorption spectrum at the region of 1653.96cm-1 signifying alpha helix but when combined with the drugs, exhibited an absorption spectrum at the region of 1603.06cm-1 which signified side absorption. At pH 5.0, sulphadoxine and pyrimethamine combination therapy induces an increase in α-helix of HbA and an increase in β-sheet structure of HbS. HbS interacts more with S-P drugs, perhaps due to a greater electrostatic and hydrophobic interaction between it and the drug followed by HbAS and HbA. There was a significant decrease in intensity of absorption observed at pH 7.2 especially with HbA and HbS as compared to what was observed at pH 5.0 which implies a reduction in the interaction with drugs.The Simultaneous qualitative and quantitative analysis of amide 1 band FTIR spectra of haemoglobin A, AS and S at pH 5.0 and pH 7.2 revealed changes in the alpha helix, beta sheet and beta turn contents of the proteins.
