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

Abstract

<p>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.</p>

The yellow and the black of synthetic melanins

“…Overall, the current observations strengthen our hypothesis that MN materials are built from at least two types of substances: 1) a soluble, yellow-to-orange colored component, rich in unoxidized precursors and 2) an insoluble, dark component. In addition, our earlier experiments [2][3] and other reports 15, 19-20, 32, 40-42 indicate that the ratio of the various reaction products generated, and/or their physic-chemical properties, may depend on the reaction conditions applied.…”

“…Building upon earlier observations and the hypotheses derived from them, we explored further the possibility that melanins (MNs), synthesized through air-oxidation in an alkaline environment, consist of at least two distinctly different types of materials. [1][2][3] We observed that from within the dark-brown to black material typically generated during the MN synthesis process, one can extract substances that possess a much lighter (orange to yellow) color. We have expanded these observations in part with the inclusion of catechol and pyrogallol as precursors for MN-like materials.…”

Appearing as eumelanin or as pheomelanin and the push towards eumelanin by cysteine.

“…[15][16][17][18][19] Our current report is a combination of results obtained from new experiments and through an evaluation of experimental data collected over the past three years; some of which have been detailed elsewhere. [20][21][22][23][24][25] In these previous reports we detailed and discussed observations that this current report expands on and integrates into one overarching theme about the balance between EuMN and PhMN:…”

“…22 2) The addition of other amino acids (AA) appeared to inhibit, but not delay, the formation of any colored material and to yield reaction mixtures with different UV-Vis absorbance profiles. 24 3) The post-synthesis precipitation of EuMN-like materials yielded supernatants that contained materials that in appearance and in other properties were PhMN-like; although no C was present during the synthesis of these materials. 23 4) Our previous observations prompted us to hypothesize that the synthesis of EuMN leads to a mixture of at least two different sets of materials.…”

“…In addition, we hypothesized that the parameters which affect the kinetics of the reaction in part determine the balance between these two sets of materials and affect the ultimate appearance of the reaction mixture: light-or dark-colored. [22][23][24] 5) Many of the results and the accompanying discussions revolve around the subjective description of the synthesized materials; particularly regarding their appearance. Thus, we developed an objective mathematical process to evaluate and compare the colors of the synthesized materials.…”