Effects of nonenzymatic glycosylation and fatty acids on tryptophan binding to human serum albumin.

The effects of bound fatty acids and nonenzymatic glycosylation (NEG) on tryptophan binding to human serum albumin (HSA) were examined utilizing a rate of dialysis technique. HSA with 0, 1, 2, 3, or 5 mol of palmitate bound per mol of HSA was glycosylated in vitro to a level exceeding that seen in diabetes. NEG was not inhibited by fatty acids, suggesting that Lys-525, the primary site for NEG, is not an essential component of the principal sites for long-chain fatty acid binding to HSA. Scatchard analysis of binding data showed an expected fatty acid dependent decrease in the number of available tryptophan binding sites, but showed that fatty acids did not affect tryptophan affinity. The binding data failed to show an effect of NEG on tryptophan binding. The lack of inhibition of tryptophan binding by NEG suggests that drug-binding Site II, the indole/benzodiazepine site, is resistant to both NEG and to any conformational changes in HSA which may occur with NEG. These data suggest that elevated plasma free tryptophan and the resulting altered serotonin metabolism seen in diabetes are independent of increased NEG and likely result from diabetic hyperlipidemia.