In situ evaluation of esterase stereoselectivity in two-dimensional electropherograms and tissue sections

Staining with both enantiomers of an alpha-naphthyl ester plus a diazonium salt and comparing the color intensities given by the two enantiomers is a convenient method to evaluate the esterase stereoselectivity for that ester in two-dimensional electropherograms and tissue sections. Application of this method for rat liver has shown that (1) several esterases, e.g., one of pI 6.4 and Mr 118 kDa, are moderately stereoselective against alpha-naphthyl (R)-N-acetylalaninate and (R)-N-methoxycarbonylalaninate but strictly stereoselective against alpha-naphthyl (S)-N-methoxycarbonylvalinate, implying that esterase stereoselectivity may be inverted by changing the ester structure; and (2) these esterases are mainly contained in the hepatocytes around central veins.