Glycation and secondary conformational changes of human serum albumin: study of the FTIR spectroscopic curve-fitting technique

The aim of this study was attempted to investigate both the glycation kinetics and protein secondary conformational changes of human serum albumin (HSA) after the reaction with ribose. The browning and fluorescence determinations as well as Fourier transform infrared (FTIR) microspectroscopy with a curve-fitting technique were applied. Various concentrations of ribose were incubated over a 12-week period at 37 +/- 0.5 degrees C under dark conditions. The results clearly shows that the glycation occurred in HSA-ribose reaction mixtures was markedly increased with the amount of ribose used and incubation time, leading to marked alterations of protein conformation of HSA after FTIR determination. In addition, the browning intensity of reaction solutions were colored from light to deep brown, as determined by optical observation. The increase in fluorescence intensity from HSA ribose mixtures seemed to occur more quickly than browning, suggesting that the fluorescence products were produced earlier on in the process than compounds causing browning. Moreover, the predominant a-helical composition of HSA decreased with an increase in ribose concentration and incubation time, whereas total I3-structure and random coil composition increased, as determined by curve-fitted FTIR microspectroscopy analysis. We also found that the peak intensity ratios at 1044 cm(-1)/1542 cm(-1) markedly decreased prior to 4 weeks of incubation, then almost plateaued, implying that the consumption of ribose in the glycation reaction might have been accelerated over the first 4 weeks of incubation, and gradually decreased. This study first evidences that two unique IR peaks at 1710 cm(-1) [carbonyl groups of irreversible products produced by the reaction and deposition of advanced glycation end products (AGEs)] and 1621 cm(-1) (aggregated HSA molecules) were clearly observed from the curve-fitted FTIR spectra of HSA-ribose mixtures over the course of incubation time. This study clearly suggests that FTIR spectroscopic curve-fitting technique may be easily used to allow determining the marked changes in the secondary conformational structure and protein aggregation of HSA during ribosylation as well as the production of AGEs.