Ultrasonic measurement of melanosomes for characterization of their physicochemical structure in B16 and Harding-Passey melanomas.

Ultrasonic measurement of the two different forms of melanosomes was carried out at 20 to 300 MHz on B16 and Harding-Passey mouse melanomas which produce ellipsoidal-lamellar and spherical-granular melanosomes, respectively. We found that the structure of the two forms is basically amorphous and copolymeric in the molecular dimension of a segment composed of 5 to 6 zigzag units. A marked difference in particle wave resonance was found around 200 MHz in the two melanosomes. Based on the chemical structure of melanin proposed by Hempel, it was indicated that the physical structure of Harding-Passey melanosomes is a copolymer in which melanin and protein moieties run parallel to each other but may bind together at the sites of planar groups, while that of B16 melanosomes 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 known as the Born-Karman periodic boundary condition in semiconductive band theory, may be related to the formation of the lamellar structure seen in B16 melanosomes.