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Vibrational Spectroscopic Studies on the Disulfide Formation and Secondary Conformational Changes of Captopril–HSA Mixture after UV‐B Irradiation
Author(s) -
Li MeiJane,
Lin ShanYang
Publication year - 2005
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2005-04-25-rn-497
Subject(s) - chemistry , captopril , raman spectroscopy , irradiation , fourier transform infrared spectroscopy , infrared spectroscopy , chromatography , crystallography , analytical chemistry (journal) , nuclear chemistry , photochemistry , organic chemistry , chemical engineering , medicine , physics , blood pressure , nuclear physics , optics , radiology , engineering
The effects of pH and ultraviolet‐B (UV‐B) irradiation on the secondary structure of human serum albumin (HSA) in the absence or presence of captopril were investigated by an attenuated total reflection (ATR)/Fourier transform infrared (FTIR) spectroscopy. The UV‐B exposure affecting the stability of captopril before and after captopril–HSA interaction was also examined by using confocal Raman microspectroscopy. The results indicate that the transparent pale‐yellow solution for captopril–HSA mixture in all pH buffer solutions, except pH 5.0∼7.0, changed into a viscous form then a gel form with UV‐B exposure time. The secondary structural transformation of HSA in the captopril–HSA mixture with or without UV‐B irradiation was found to shift the maxima amide I peak in IR spectra from 1652 cm −1 assigned to α‐helix structure to 1622 cm −1 because of a β‐sheet structure, which was more evident in pH 3.0, 8.0 or 9.0 buffer solutions. The Raman shift from 1653 cm −1 (α‐helix) to 1670 cm −1 (β‐sheet) also confirmed this result. Captopril dissolved in distilled water with or without UV‐B irradiation was determined to form a captopril disulfide observed from the Raman spectra of 512 cm −1 , which was exacerbated by UV‐B irradiation. There was little disulfide formation in the captopril–HSA mixture even with long‐term UV‐B exposure, but captopril might interact with HSA to change the protein secondary structure of HSA whether there was UV‐B irradiation or not. The pH of the buffer solution and captopril–HSA interaction may play more important roles in transforming the secondary structure of HSA from α‐helix to β‐sheet in the corresponding captopril–HSA mixture than UV‐B exposure. The present study also implies that HSA has the capability to protect the instability of captopril in the course of UV‐B irradiation. In addition, a partial unfolding of HSA induced by pH or captopril‐HSA interaction under UV‐B exposure is proposed.