ORGANOPHOSPHATE SENSITIVE AND INSENSITIVE CARBOXYLESTERASES IN HUMAN SKIN

The influence of paraoxon and bis(4-nitrophenyl)phosphate (BNPP) on ca rboxylesterases of human skin is assayed. Both organophosphates have f requently been used as inhibitors of carboxylesterases of the B-estera se type. Homogenates from carefully washed skin have no paraoxon-cleav ing activity and very little phosphodiesterase activity with BNPP. How ever, a number of skin enzymes are irreversibly inhibited by these com pounds. Three zones of carboxylesterase bands can be detected in the s oluble fraction of skin homogenate by isoelectric focusing. One zone c ontaining 5 esterase bands in the pI-range of 6.7-7.0 and another zone at pI 4.9 are insensitive to organophosphate inhibition. The zone wit h the main esterase activities contains at least 6 bands in the range of pI 5.7-6.2. All of these are quickly and completely inhibited by pa raoxon. The complex inhibition kinetics with BNPP and observations wit h differing substrates point to a functional heterogeneity. The estera ses with pI-values in the range of 5.7 to 6.2 and the esterase with pI 4.9 can be enriched using anion exchange chromatography and FPLC. Fro m the data presented here it is concluded that human skin contains at least four different carboxylesterases which act on simple aromatic es ters.