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Tyrosinase-mediated Inhibition of in Vitro Leucine Incorporation into Mouse Melanoma by 4-Isopropylcatechol¹

Department of Dermatology, Harvard Medical School, and Massachusetts General Hospital, Boston, Massachusetts 02114

The effect of 4-isopropylcatechol (4-IPC), a potent, irreversible cutaneous depigmenting agent, on protein biosynthesis of malignant melanoma cells in mice was studied by examining the in vitro amino acid (leucine) incorporation into a microsome fraction in cell sap. The present study revealed that 4-IPC does not inhibit the protein biosynthesis of the cell-free system in mouse liver, but remarkably inhibits it in mouse melanoma cells, which contain a high level of tyrosinase. The enhanced inhibition was found also in the mouse liver cell-free system when tyrosinase was added. Air oxidation products of 4-IPC were not responsible for such inhibition. These results may indicate that 4-IPC directly inhibits protein biosynthesis, probably by some intermediates that occur in an early stage of enzymatic oxidation of 4-IPC.

¹ This work was supported by USPHS Grants CA12108 and CA13651.

² Present address: Department of Biochemistry, Faculty of Science and Medicine, Niigata University, Niigata, Japan.

Received 5/16/75. Accepted 8/ 1/75.