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Biochem J. 2005 Oct 15;391(Pt 2):249-59.

Mutations in dopachrome tautomerase (Dct) affect eumelanin/pheomelanin synthesis, but do not affect intracellular trafficking of the mutant protein.

Author information

1
Pigment Cell Biology Section, Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health (NIH), Bethesda, MD 20892, USA.

Abstract

Dopachrome tautomerase (Dct) is a type I membrane protein and an important regulatory enzyme that plays a pivotal role in the biosynthesis of melanin and in the rapid metabolism of its toxic intermediates. Dct-mutant melanocytes carrying the slaty or slaty light mutations were derived from the skin of newborn congenic C57BL/6J non-agouti black mice and were used to study the effect(s) of these mutations on the intracellular trafficking of Dct and on the pigmentation of the cells. Dct activity is 3-fold lower in slaty cells compared with non-agouti black melanocytes, whereas slaty light melanocytes have a surprisingly 28-fold lower Dct activity. Homology modelling of the active site of Dct suggests that the slaty mutation [R194Q (Arg194-->Gln)] is located in the active site and may alter the ability of the enzyme to transform the substrate. Transmembrane prediction methods indicate that the slaty light mutation [G486R (Gly486-->Arg)] may result in the sliding of the transmembrane domain towards the N-terminus, thus interfering with Dct function. Chemical analysis showed that both Dct mutations increase pheomelanin and reduce eumelanin produced by melanocytes in culture. Thus the enzymatic activity of Dct may play a role in determining whether the eumelanin or pheomelanin pathway is preferred for pigment biosynthesis.

PMID:
15960609
PMCID:
PMC1276922
DOI:
10.1042/BJ20042070
[Indexed for MEDLINE]
Free PMC Article

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