XII International Pigment Cell Conference: Part II

An ultrasonic measurement of melanosomes was carried out in frequencies from 0.333 MHz to 300 MHz on B16 and Harding-Passey (HP) mouse melanomas, which produce two different forms of melanosomes, i.e., ellipsoidal-lamellar melanosomes in B16 and splherical-graniular melanosomes in HP. We found that the structure of the two melanosomes is basically amorphous and co-polymeric in the molecular dimmension of a segment composed of five to six zigzag units. Stochastic resonance was, however, markedly different between B16 and HP melanosomes, indicating that the structure of the B16 melanosome is moderately packed, while that of the HP melanosome is more open and similar to that of the sepia melanosome. A marked difference of particle wave resonance was also found around 200 MHz in the twomelanosomes. It wasindicated, based on the chemical structure of melanins proposed by Hempel, that the physical structure of the HP melanosome is a co-polymer in which melanin and protein moieties run parallel to each other but may bind together at the sites of planar groups, while that of the B16 melanosome is a double-helix polymer of melanin and protein moieties with a screw symmetry of N = 6. This type of one-dimensional cyclic ordering, commonly knowln as Born-Karman periodic boundary condition in semiconductive band theory, may be related to the formation of the lamellar structure seen in the B16 melanosome.