Characterization of arginase activity from mouse epidermis and its relation to ornithine decarboxylase induction by the tumor-promoting agent, 12- O-tetradecanoylphorbol-13-acetate

Abstract

Arginase, which catalyzes the cleavage of l-arginine to urea and ornithine, was detected in both soluble and particulate fractions of mouse epidermis. In a typical experiment, about 75 and 25% of the total arginase activity was associated with the soluble (100 000 × g supernatant) and the washed particulate fraction, respectively. Both soluble and particulate enzymes required the presence of divalent Mn 2+ for activity. Arginase activity was increased by about 50% in the particulate fraction, but not in the soluble fraction, by preheating the fractions at either 50 or 55°C in the presence of 15 mM MnCl 2. Enzyme activity in both fractions, in the absence of 15 mM MnCl 2, dropped precipitously during heating. A comparison of the nature of arginases in the soluble and particulate fractions revealed similar K m values (13 mM) and pH optima (9.5) and identical heat denaturation curves. Application of 10 nmol of 12- O-tetradecanoylphorbol-13-acetate to mouse skin did not increase arginase activity in either fraction over a period of 24 h. In contrast, there was a large increase in ornithine decarboxylase activity in the soluble fraction 4.5 h after treatment. Mouse epidermal ornithine decarboxylase activity was much less than arginase activity and was predominantly localized in the soluble fraction. These results indicate that the normal level of arginase activity is not a limiting factor for the stimulation of polyamine biosynthesis by TPA. High arginase activity in mouse epidermis may play a role in providing ornithine for polyamine biosynthesis and in the production of glutamate and proline as well as in the production of keratinous proteins.