Hydrolysis of parabenes by extracts from differing layers of human skin.

We could distinguish four carboxylesterases capable of hydrolyzing 4-hydroxy-benzoic acid esters in human skin and subcutaneous fat tissue. The highest specific activities were found in an extract from subcutaneous fat tissue. The most prominent esterase of this tissue prefers the methyl ester of 4-hydroxybenzoic ester (methyl parabene). Its activity decreases with increasing chain length of the alcohol moiety of the parabenes. The existence of a second parabene esterase in subcutaneous fat is concluded from organophosphate inhibition characteristics. Another prominent parabene esterase was characterized in extracts from transformed keratinocytes. It prefers butyl parabene and its activity decreases with decreasing chain length of the alcohol moiety. The fourth parabene esterase is an enzyme of blood which contaminates the tissue extracts used here. All of the tissue extracts were active at pH 8.0, no parabene hydrolyzing activity could be demonstrated at pH 5.0.