How should the extinction coefficient for absorption of melanin be expressed?
The molecular structure of the extended melanin polymer is neither well characterized nor unique, so citing the concentration as [moles/liter] is difficult. There is possibly some degree of protein incorporation in the polymer, so citing the concentration as [mg/ml] may be misleading. • How does one encounter melanin? Melanin is synthesized enzymatically at roughly 10-nm granular sites studding the internal walls of the melanosome, a roughly 1-µm diameter organelle. Melanosomes may contain a variable amount of melanin. The melanosomes of the retinal pigmented epithelium (RPE) have a very dense concentration of melanin. Cutaneous melanosomes are variable and may have 1/4th to 1/10th the melanin concentration of the RPE melanosomes. And there are some melanosomes devoid of melanin. • How are melanosomes distributed? The volume fraction of melanosomes in a particular epithelial layer, such as the cutaneous epidermis or the RPE, can vary. The average epidermal absorption coefficient depend
