Metabolism of prednisolone 21-acetate in hairless mouse skin

We investigated the hydrolytic activity of prednisolone 21-acetate (PNA) to prednisolone (PN) in an enzyme solution composed of esterase and skin homogenates from hairless mice. The values of the Michaelis-Menten constant obtained from hairless mouse skin and esterase solution were 14.2 and 10.2 microM, respectively; conversely, the value of the maximum rate from hairless mouse and esterase solution were 0.67 and 1,886 nmol/min/mg protein, respectively. To examine the effect of enzymatic inhibitors on hydrolytic activity, five enzymatic inhibitors, 3,4-dichloroisocoumarine (DCIC), N-tosyl-L-phenylalanine chloromethyl ketone, iodoacetamide, p-hydroxymercuribenzoic acid (HMBA) and sodium dodecylsulfate, were added to the enzyme solution. Sixty-eight percent of hydrolytic activity in skin homogenates were not deactivated by DCIC which completely inhibited the enzymatic activity in esterase solution. We also studied the localization of hydrolytic enzyme with a subcellular faction: 66 and 11% of specific activity existed in microsome (Ms) and cytosol (Cp) fractions, indicating that the hydrolytic activity of PNA was included mainly in the Ms fraction. Hydrolytic activity in Ms and Cp fractions was different from sensitivity to enzymatic inhibitor; DCIC inhibited activity in the Ms fraction and, on the other hand, HMBA inhibited it in the Cp fraction. Therefore, Ms and Cp fractions in skin homogenates include a different esterase isoform and the metabolism of PNA to PN in hairless mouse skin is mediated by these isoforms.