Ascorbate induced lipid peroxidation results in loss of receptor binding in Tris, but not in phosphate, buffer. Implications for the involvement of metal ions

Rat brain homogenate was incubated with various concentrations of ascorbate in a Tris-HCl buffer. Thiobarbituric acid-reactive substances (TBARS) were measured and ³H-QNB (quinuclidinyl benzilate) binding was also assayed on the same homogenate. Good parallelism between TBARS formation and loss of ³H-QNB binding activity confirmed that loss of ³H-QNB binding resulted from ascorbate-induced lipid peroxidation. However, neither formation of TBARS nor loss of ³H-QNB binding occurred in phosphate buffer or in the Tris-HCl system in the presence of metal-chelating reagents. This indicates that phosphate addition prevents the ascorbate effects due to complete chelation of intrinsic metal ions.