ESTER HYDROLYSIS AND CONJUGATION REACTIONS IN INTACT SKIN AND SKIN HOMOGENATE, AND BY LIVER ESTERASE OF RABBITS

1. Procaine, 2-chloroprocaine, ethyl aminobenzoate and methyl salicylate were added at various concentrations to liver esteraste, supernatant of skin homogenate, or single-pass perfused ears of rabbits. 2. V(max) of product formation by purified liver esterase correlated with the rank order of the distribution coefficients (n-octanol/buffer) of the substrates and ranged between 11 and 1100 pmol/min per mug protein. K(m) values were between 20 and 50 muM. 3. No correlation was observed when the apparent enzyme kinetics, calculated by nonlinear adaptation, were compared with each other after substrate administration to skin, arterial influx, or incubation with skin homogenate. 4. An acid labile conjugate of ethyl 4-aminobenzoate was found, mainly during arterial perfusion and in supernatant of skin homogenate, after administration of ethyl 4-aminobenzoate. 5. Acetamidobenzoic acid was observed in quantities of about 10% of the free 4-aminobenzoic acid during dermal or arterial application of procaine. This metabolite was not found with ethyl 4-aminobenzoate. 6. The results from isolated rabbit ear perfusion differ quantitatively and qualitatively with those obtained from supernatant of skin homogenate or purified liver esterase.