Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.10.3.1 (tyrosinase)
 9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Among the various melanin-producing systems, the ink gland of the cuttlefish (Sepia officinalis) has traditionally been regarded as a most convenient model system for the studies of melanogenesis. The ink gland is a highly specialized organ with immature cells in the inner portion, from where the cells gradually mature, migrate towards the outer portion of the gland and become competent to produce melanin giving rise to particulate melanosomes. When cell maturation is complete, melanin is secreted into the lumen of the gland, accumulated into the ink sac and ejected on demand. Biochemical studies carried out over the past two decades have shown that the ink gland contains a variety of melanogenic enzymes, including tyrosinase, a peculiar dopachrome rearranging enzyme (which catalyses the rearrangement of dopachrome to 5,6-dihydroxyindole) and a peroxidase (presumably involved in the later stages of melanin biosynthesis). These enzymes are functionally interactive in close subcellular compartments of ink gland cells and appear to act in a concerted fashion during the process of melanogenesis in the mature portion of the gland. More recent studies have revealed that ink production and ejection are affected and modulated by the N-methyl-D-aspartate (NMDA)-nitric oxide (NO)-cyclic GMP (cGMP) signalling pathway. Glutamate NMDA receptor and NO synthase, the enzyme responsible for the synthesis of NO, have been detected by biochemical and immunohistochemical techniques in immature ink gland cells. Stimulation of NMDA receptors caused a marked elevation of cGMP levels, activation of tyrosinase and increased melanin synthesis in the mature portion of the gland, via the NO-guanylyl cyclase interaction. This signalling is also present in different regions of the nervous system in Sepia and in certain neural pathways controlling contraction of the ink sac sphincters and wall muscle in the ejection mechanism. Overall, these and other findings allowed elaboration of an improved model of melanin formation in Sepia, which underscores the complex interplay of melanogenic enzymes and regulatory factors, highlighting both the similarities and the differences with melanogenesis in mammals.
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PMID:Melanogenesis in the ink gland of Sepia officinalis. 1295 Jul 31

The biosynthesis, localization and fate of catecholamines in the ink gland of the cuttlefish Sepia officinalis were investigated by combined biochemical and immunohistocytochemical methodologies. HPLC analysis of crude ink gland extracts indicated the presence of dopa (2.18+/-0.82 nmol/mg of protein) and DA (dopamine, 0.06+/-0.02 nmol/mg of protein), but no detectable noradrenaline or adrenaline. DA was shown to derive from L-tyrosine, according to experiments performed by incubating intact ink glands with [L-14C]tyrosine. The biosynthetic process involves a tyrosine hydroxylase and a dopa decarboxylase pathway and is independent of tyrosinase. The tyrosine hydroxylase activity was detected under conditions of tyrosinase suppression in the cytosolic fraction, but not in the melanosomal fraction, of ink gland extracts, and the presence of the enzyme was confirmed by Western-blot analysis. Dopa and DA were found to be released from the ink glands by processes controlled through the NMDA-nitric oxide-cGMP (where NMDA stands for N -methyl-D-aspartate) signalling pathway, as apparent from incubation experiments performed with [L-14C]tyrosine in the presence of NMDA, diethylamine NONOate (diethylamine diazeniumdiolate), a nitric oxide donor, 8-bromo-cGMP or a guanylyl cyclase inhibitor. Immunohistochemical results coupled with electron microscopy indicated that DA was concentrated in vesicles specifically localized in the mature melanin-producing cells of the ink gland proximal to the lumen and separated from the melanin-containing melanosomes. NMDA receptor stimulation or exposure to an NO donor caused a marked loss of DA immunoreactivity in mature cells, consistent with a release process. In the lumen of the ink gland, where mature exhausted cells pour their contents, DA immunoreactivity was found to be associated with the melanin granules, due apparently to physical adsorption. Overall, these results point to DA as a marker of cell maturation in Sepia ink gland subject to release by the NO/cGMP signalling pathway, and disclose apparently overlooked DA-melanin interactions in secreted ink of possible relevance to the defence mechanism.
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PMID:Dopamine in the ink defence system of Sepia officinalis: biosynthesis, vesicular compartmentation in mature ink gland cells, nitric oxide (NO)/cGMP-induced depletion and fate in secreted ink. 1467 74