TYROSINE UTILIZATION BY CULTURED MELANOMA-CELLS - ANALYSIS OF MELANIN BIOSYNTHESIS USING [TYROSINE-C-14 AND [THIOURACIL-C-14

Melanin pigment synthesis was investigated using RPMI 3460 hamster melanoma cell cultures. Optimal conditions for melanin synthesis were established and synthesis was correlated with tyrosine uptake. We observed that melanin did not undergo intracellular degradation, that the pool of melanin synthetic intermediates was very small and short-lived, and that the incorporation of both dl-[2-14C]tyrosine and 2-[2-14C]thiouracil into melanin probably reflected the actual rate of synthesis. Considerable melanin synthesis occurred in the absence of exogenous tyrosine. Experiments with cycloheximide indicated that while tyrosine incorporation into protein was inhibited >98%, melanin synthesis was enhanced approximately 30%. The stimulation cannot be explained by a change in tyrosinase activity, or by alterations in the intracellular tyrosine pool size. Stimulation was immediate and occurred even in the absence of exogenous tyrosine. Compartmentalized tyrosine may be used for this enhanced melanin synthesis. © 1979.