NMR study of lipoic acid binding to bovine serum albumin.

Evidence for the binding of lipoic (LA) and dihydrolipoic (DHLA) acid to bovine serum albumin (BSA) was sought as a feature for understanding the mechanism of their antioxidant activity and prevention of glycation. Experiments were performed by 1H high resolution NMR. The average binding ratio of LA, DHLA and tetranor LA to BSA were 10 +/- 2, 7.9 +/- 2 and 1.8 +/- 0.4 mol/mol BSA respectively. In this row the number of bound molecules lessens with the decrease of their hydrophobic interactions that correlates with their protective activity. Octanoic acid, the closest analog of lipoate, had a binding ratio of 4.7 +/- 0.5 mol. Lipoic acid was able to replace bound octanoic acid which points out that lipoate occupies the same binding site on BSA. Lipoate had no binding to low density lipoproteins extracted from human plasma which corresponds to its low protection of LDL against glycosylation and oxidative modification. This study indicates that lipoic acid molecules experience strong hydrophobic attraction and binding to BSA which is important part of lipoate protective mechanism.