Abstract
1. Procaine, 2-chloroprocaine, ethyl aminobenzoate and methyl salicylate were added at various concentrations to liver esterase, supernatant of skin homogenate, or single-pass perfused ears of rabbits. 2. Vmax 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 micrograms protein. Km values were between 20 and 50 microM. 3. No correlation was observed when the apparent enzyme kinetics, calculated by non-linear 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.
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