Metabolism of sulphobromophthalein I: positional isomers of sulphobromophthalein monoglutathione conjugate

Three positional isomers of sulphobromophthalein glutathione monoconjugate (BSP-mGSH) were detected using a paired-ion HPLC method that employs trieth ylamine phosphate (TEA-H3PO4) as a pairing agent. To confirm that these com pounds were glutathione (GSH) conjugates, sulphobromophthalein (BSP) was in cubated with a four-fold volume of GSH under alkaline ammonium hydroxide. A t least 6 metabolites (3 di-GSH conjugates and 3 isomers of mono-GSH conjug ates) were produced under these conditions. The three mono-GSH conjugates w ere each purified and identified as compounds with a molecular weight of 10 20 according to FAB mass spectrometry results. Positional isomers of BSP-GS H were provisionally distinguished via the addition of the symbols alpha, b eta and delta to the end of each abbreviation, to reflect the amount of iso mers present. Thus, the isomer present in the largest quantity was termed B SP-mGSH(alpha), the second most abundant isomer was termed BSP-mGSH(beta) a nd the third was termed BSP-mGSH(delta). Interestingly, a species differenc e was recognized in that rat cytosol GSH S-transferase (CST) primarily prod uced BSP-mGSH(alpha), whereas guinea-pig cytosol generated BSP-mGSH(delta), BSP-mGSH(alpha) and BSP-mGSH(beta) equally and rabbit cytosol mainly produ ced BSP-mGSH(beta).