Abstract
It was discovered that the indophenol dyes produced a pallor in amphibian larvae raised in solutions of these dyes. 1 This suggested the possibility of solving many of the fundamental problems of pigment formation through a study of the mechanism of action of these dyes. The original work was repeated and confirmed, but extreme variation was found with regard to the effectiveness of the dyes in different species. 2 It was also proved conclusively that the dyes do not exert an influence on pigment via the hypophysis.
The present paper gives the results of experiments devised to test the hypothesis that the dyes acted directly on the pigment granules by destroying them after they were formed or by inhibiting their formation.
In preliminary experiments it was found that phenol indophenol (sodium benzenone indophenol) does not destroy pigment from the following sources: 1. Artificial pigment produced by the oxidation of either dihydroxyphenyl alanine or tyrosine. 2. Natural pigment in colloidal solution produced by brushing pigment out of the choroid coat of frozen ox eyes. 3. Natural pigment contained in melanophores in pieces of dead amphibian skin.
It was concluded from these experiments that the dye does not destroy or dissolve pigment granules after they are formed. It was thought that the dye might be inducing the pallor by influencing the enzymes responsible for pigment formation. Since tyrosinase has not been conclusively demonstrated in vertebrate forms, while dopa oxidase has, it has been assumed by many 3 , 4 , 5 that dopa oxidase is the enzyme responsible for pigment formation. Contrary to expectations, it was found that the dye did not inhibit the dopa reaction, but accelerated and intensified it. In addition, it accelerated the auto oxidation of dihydroxyphenyl alanine to dopa melanin.
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