| Popis: |
Modern investigators of pigment agree that the formation of pigment in the melanoblasts of ectodermal and mesodermal origin is due to the oxidation of a colorless propigment by an enzyme. Fuerth has shown that this melanogen is most probably a cyclic protein component. Fuerth, Przibram, Onslow and others first proposed tyrosine as the melanogen. Free tyrosine has been demonstrated in the circulation of the higher vertebrates, but tyrosinase has been found in insects and cold-blooded animals only. There is no positive evidence that tyrosine is the mother substance of melanin in warm-blooded animals, especially in man. In recent years a number of Italian authors (Angeli, Saccardi, Rondoni, Gallerani, Quattrini and Introzzi) have maintained that pyrole and its derivatives, such as α-methylindole and scatole, are also propigments. The fallacy of their conclusions has been brought out by the work of Bloch and Schaaf 1 and of Peck. 2 Bloch 1 has |
