FT-IR spectroscopy of natural melanins isolated from Harding-Passey mouse melanoma

The alterations caused on the structure of melanins by acid and alkaline extraction methods were studied by means of techniques such as Fourier Transform Infrared spectroscopy and thermogravimetry. Acid extraction results in the hydrolysis of aromatic monomers of the pigment, leading to uncyclicized residues and to a less conjugated polymer. Alkaline methods catalyse the covalent binding of proteins present in the melanin extract, thus leading to melanoprotein artifacts. A new method based on the delipidation with ether and deproteinization with SDS of previously isolated melanosomes is proposed. This method shows that melanins present in Harding-Passey mouse melanoma have a bound protein moiety, so that they should exist "in vivo" as melanoprotein complexes. Thermogravimetric data suggest that the chromogen moiety of the melanoproteins in Harding-Passey mouse melanoma is a mixture of eu- and pheomelanins.