Kinetic Study of the Melanogenesis from Select Catecholamines in the Presence of L-Cysteine or Other Amino Acids

This report is a continuation of an earlier report on the effect of L-cysteine on the synthesis of melanin-like materials from catecholamines. We confirmed the pattern of results indicating that in the presence of L-cysteine the appearance of dark colors during the melanogenesis reactions is delayed, but that ultimately the presence of L-cysteine yields reaction mixtures with darker colors. The results of the current report indicate that the effect of L-cysteine is very reproducible in the cases of DOPA or dopamine, but much more variable in the cases of norepinephrine or epinephrine. The delays in color formation in the cases of norepinephrine and epinephrine were much longer compared to the cases of DOPA and dopamine. In addition to L-cysteine, we tested the effect of a few amino acids on the melanogenesis reactions. In general, we observed that the presence of the amino acids slowed, but did not delay the color formation. Given enough reaction time, the presence of amino acids did result in reaction mixtures exhibiting darker colors. In addition, some of the results obtained indicated a difference between a-amino acids and their corresponding primary amines, e.g., tyrosine vs. tyramine.