Factors affecting measurement of aryl hydrocarbon hydroxylase activity in mouse skin

Mouse skin exhibits relatively high aryl hydrocarbon hydroxylase (AHH) activity when measured under optimal conditions. The enzyme is unequally distributed in the cutaneous layers with the highest concentration in the epidermis. Subcellularly, it is localized in the microsomal fraction. As much as two-thirds of the enzymatic activity was destroyed when harsh homogenization techniques were used during tissue preparation. Incorporation of the reduced pyridine nucleotide NADH into an incubation mixture containing NADPH increased epidermal AHH activity by one-third. When methods that maximize activity were employed, the AHH activities of skin of C57BL/6 inbred mice and of ICR Swiss random-bred mice were 5 to 10 times as active as lung tissue and about one-tenth as active as liver.