Organophosphate sensitive and insensitive carboxylesterases in human skin

Abstract

The influence of paraoxon and bis(4-nitrophenyl)phosphate (BNPP) on carboxylesterases of human skin is assayed. Both organophosphates have frequently been used as inhibitors of carboxylesterases of the B-esterase type. Homogenates from carefully washed skin have no paraoxon-cleaving activity and very little phosphodiesterase activity with BNPP. However, a number of skin enzymes are irreversibly inhibited by these compounds. Three zones of carboxylesterase bands can be detected in the soluble fraction of skin homogenate by isoelectric focusing. One zone containing 5 esterase bands in the p I-range of 6.7–7.0 and another zone at p I 4.9 are insensitive to organophosphate inhibition. The zone with the main esterase activities contains at least 6 bands in the range of p I 5.7–6.2. All of these are quickly and completely inhibited by paraoxon. The complex inhibition kinetics with BNPP and observations with differing substrates point to a functional heterogeneity. The esterases with p I-values in the range of 5.7 to 6.2 and the esterase with p I 4.9 can be enriched using anion exchange chromatography and FPLC. From the data presented here it is concluded that human skin contains at least four different carboxylesterases which act on simple aromatic esters.