Chapter 4 123 a Transmission Electron Microscope (TEM) where the melanosome granules can clearly be seen throughout the cortex of the fiber. The chromophores of the melanosomes are formed in the hair follicle, biosynthesized from tyrosine using a tyrosinase enzyme to form dopaquinone. If cysteine is present during the biosynthesis, pheomelanin will predominate without cysteine, eumelanin will predominate. The basic chromophoric units for eumelanin are dihydroxyindole (DHI) and dihydroxyindole-2-carboxylic acid (DHICA), and for pheomelanin are benzothiazines, shown here.5 Figure 1 TEM micrograph of dark hair showing eumelanin granules N S CO2H NH 2 HO HO2C S N HO2C HO CO 2 H NH2 Benzothiazines H N HO HO H N HO HO CO2H DHI DHICA