Abstract
The binding of thiamin to two kinds of melanins, one separated from carp eye tissues and the other synthesized from tyrosine, was measured in the presence of various drugs : chlorpromazine, kanamycin, chloroquin, streptomycin, paraquat, hidralazine, quinidine, nortriptyline, amitriptyline and imipramine. All of these drugs strongly inhibited the binding of thiamin to both melanins at high concentrations over 1 mM of the drugs, and the inhibition degree varied with the kind of drugs. Some of the drugs also induced the release of thiamin bound to melanin of eye in vivo. The binding curves were constructed for thiamin and chlorpromazine by both of the melanin sample. Thiamin showed regular Langmuir type binding, while chlorpromazine showed strong cooperative binding. Though the intrinsic binding constant was much higher for thiamin than for chlorpromazine, more chlorpromazine than thiamin bound to both melanins at high concentrations as a result of the cooperative binding. We concluded that competitive binding of drugs induced the inhibition of thiamin binding to melanin, as well as the release of thiamin bound to melanin in vivo.
