The Journal of Biochemistry
Online ISSN : 1756-2651
Print ISSN : 0021-924X
The Reciprocal Relationship between Melanization and Tyrosinase Activity in Melanosomes (Melanin Granules)
MAKOTO SEIJITHOMAS B. FITZPATRICK
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JOURNAL FREE ACCESS

1961 Volume 49 Issue 6 Pages 700-706

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Abstract

1. Melanosomes, the distinctive, en-zymically active particles which are the site of melanin formation, have been separated from B-16 and Harding-Passey mouse mela-noma and from retinal pigment-epithelium of chick embryos by density-gradient cen-trifugation.
2. The color and tyrosinase activity per milligram of protein-nitrogen of melanosomes isolated from these tissues have been com-pared. Melanosomes isolated from B-16 mouse melanoma showed greater optical density and less tyrosinase activity than those of Harding-Passey melanoma. Melanosomes isolated from the retinal pigment-epithelium of the 10-day-old chick embryo showed less optical density and higher tyrosinase activity than those isolated from the retinal pigment-epithelium of the 17-day-old chick embryo.
3. Melanosomes isolated from Harding-Passey mouse melanoma were melanized in vitro by incubation with dopa. The reaction velocity of tyrosinase in melanosomes which had been thus melanized in vitro was signifi-cantly decreased. There was an inverse linear relationship between the concentration of dopa in the incubation mixture and the reac-tion velocity of tyrosinase.
4. Under the electronmicroscope, melano-somes which had been melanized in vitro had an intensely electron-dense appearance which suggested that their surface had been covered chemically and mechanically by dopa-melanin which had been produced during incubation.
5. Experimental results suggest that as successive layers of melano-protein accumulate on the melanosome, the active centers of tyrosinase are blocked and that therefore there exists a reciprocal relationship between degree of melanization and level of measurable tyrosinase within the melanosome.
The authors wish to thank Dr. M. S. C. Birbeck of the Chester Beatty Research Institute of London, for taking the electronmicrographs and for his valuable suggestions. They also want to express their apprecia-tion of the help given by Drs. H. Blaschko and R. Baker of Oxford University during the later phases of this investigation.
This investigation was supported in part by the Damon Runyon Cancer Fund and by Research Grant #8196-2 from the United States Public Health Service.

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© The Japanese Biochemical Society
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