ENANTIOSPECIFICITY OF COVALENT ADDUCT FORMATION BY BENZO[A]PYRENE ANTI-DIOL EPOXIDE WITH HUMAN SERUM-ALBUMIN

Human serum albumin was reacted with the (+)- and (-)-enantiomers of y -t-9,t-10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene to determine if the chiral nature of the protein influences adduct formation. The alkylate d proteins were analyzed directly by fluorescence line narrowing spect roscopy, and their spectra were compared to those of the model synthet ic adducts 8,t-9,c-10-tetrahydrobenzo[a]pyren-10-yl)histidine and oxy- r-7,t-8,t-9,c-10-tetrahydrobenzo[a]pyren-10-yl N-t-BOC-alaninate ester . The results from these analyses indicated that different adducts wer e formed by the enantiomers of the diol epoxide. The adducted proteins were also enzymatically digested, and the droxy-7,8,9,10-tetrahydrobe nzo[a]pyrene-containing adducts and hydrolysis products were isolated by boronate affinity chromatography. Diode array UV, fast atom bombard ment, and on-line atmospheric pressure ionization-mass spectral analys is of the HPLC purified products indicated that the more mutagenic and tumorigenic (+)-enantiomer forms carboxylic ester adducts with the pr otein at either Asp(187) or Glu(188), while the (-)-enantiomer forms N -tau-histidine adducts at His(146). This previously unrealized enantio specificity of the reaction of benzo[a]pyrene anti-diol epoxide with h uman serum albumin has important consequences for the application of t he adducts as biomarkers of internal exposure.