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)

Quantitative differences in the tyrosinase activity are found at the three types of malignant melanoma of Clark and Mihm by the combined 3,4-dihydroxyphenylalanine-premelanin-reaction. Only a very small activity is present in the junction nevus. In the superficial spreading melanoma the tyrosinase activity is clear, but limited. The lentigo maligna melanoma shows an increased pigmentation. The topmost activity after incubation however is present in the nodular melanoma.
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PMID:Tyrosinase activity in three types of the malignant melanoma: superficial spreading melanoma, lentigo maligna melanoma and nodular melanoma. 5 Jul 62

The concentrations of dopa and 5-S-cysteinyldopa were determined in the various cell fractions of Harding-Passey melanomas. Dopa was present in larger amounts than was 5-S-cysteinyldopa in all cell fractions, but the dopa/5-S-cysteinyldopa ratio was lower in the soluble fraction and in the small-granule fraction than in the large-granule fraction. The soluble fraction contained the greatest amount of catechols. These findings are compatible with high tyrosinase activity not only in the melanosomes but also in the small-granule and soluble fractions.
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PMID:Intracellular distribution of dopa and 5-S-cysteinyldopa in Harding-Passey melanoma. 7 Sep 22

Previous reports have shown that the tyrosinase activities of melanosomes and soluble tyrosinase isolated from melanoma were diminished when these preparations were incubated with 3,4-dihydroxyphenylalanine (dopa). It was concluded from these results that the tyrosinase activities of these preparations decreased when melanin was synthesized in these systems. The present investigation has revealed that melanin synthesized in vitro from dopa formed a complex with purified mushroom tyrosinase. The addition of melanin diminished the tyrosinase activity of the sample. These results show that the formation of the melanin-tyrosinase complex results in a decrease in the activity of the tyrosinase solution. The tyrosinase activity of the melanin-tyrosinase complex could not be increased by certain procedures which were previously found to enhance the tyrosinase activity of isolated melanosomes.
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PMID:Formation of melanin-tyrosinase complex and its possible significance as a model for control of melanin synthesis. 7 46

The hypothesis that only melanosomal catecholic amino acids contribute to melanin formation was tested by studying adult bovine eyes in which pigment synthesis is considered to be low or absent. Dopa and 5-S-cysteinyldopa were investigated in different cell fractions of the choroid and retinal pigment epithelium of cattle. Most of the dopa and 5-S-cysteinyldopa was found in the cytoplasm and very little in the large granule fraction. The presence of cysteinyldopa in the adult eye is evidence of tyrosinase activity, but the catechol amino acids in the cytoplasm probably do not give rise to melanin formation. It is assumed that they instead are excreted from the cells.
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PMID:Intracellular distribution of dopa and 5-S-cysteinyldopa in pigment cells with minimal pigment formation. 9 51

A new technique based on liquid phase ion exchange chromatography on short column is proposed for quantitative determination of tyrosine and Dopa. alpha-Amino,beta-guanidinopropionic acid is used as an internal standard of coloration. The role of H2O2 and ascorbic acid on tyrosine and Dopa was checked. Ascorbic acid prevents the auto-oxidation of Dopa, H2O2 has no effect on tyrosine but oxidizes Dopa even in the presence of excess ascorbic acid. This method was tested in mushroom tyrosinase, with and without ascorbic acid. Assays performed with tyrosinase from rabbit ocular extracts clearly showed that they do oxidize tyrosine. Reliability of the method is comparable to radioassay.
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PMID:A rapid quantitative analysis of tyrosine and its oxidation products by tyrosinase. 11 92

Both 3,4-dihydroxyphenylalanine and 2,4,5-trihydroxyphenylalanine were oxidized with periodate and mushroom tyrosinase to determine whether the latter compound is an intermediate in melanin biosynthesis. Matrix analysis of the spectra obtained with a rapid scan spectrophotometer and comparison of the spectra of quinone intermediates with model quinones disclosed that, although 2,4,5-trihydroxyphenylalanine can be oxidized to 2-carboxy-2,3-dihydroindole-5,6-quinone (dopachrome), this oxidation proceeds through a stable intermediate, 5-(2-carboxy-2-aminoethyl)-2-hydroxy-1,4-benzoquinone, which does not appear in the oxidation of 3,4-dihydroxyphenylalanine to dopachrome. Thus, these studies are in agreement with the original postulate, that 4-(2-carboxy-2-aminoethyl)-1,2-benzoquinone and leukodopachrome are the intermediates in the major pathway for dopachrome synthesis.
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PMID:The role of 2,4,5-trihydroxyphenylalanine in melanin biosynthesis. 19 58

Conley et al., in 1971, described a special type of melanoma characterized by a superficial melanic lesion at the onset; repeated local relapses as subcutaneous tumorations with an histological picture closely resembling an atypical fibroxantoma or fibrosarcoma. After a review of all the published material the autors presents a personal case with the clinical, histological and evolutive characteristics of this disease. The most interesting findings of the published case are the following: The special stains for the melanocytes (silver stain, Dopa, tyrosinase and cholinesterase) were all negative. There was an intense positivity for the lisosomal enzymes (non specific sterases, and acid phosphatases). The ultrastructural study of the tumoral tissues as well as the cells of cultures showed abundant cells with tumoral aspects, with prominent nucleoli somewhat dilated granular endoplasmic reticulum, myelin-like figures, lipidic vacuoles and abundant lisosomes. No melanosomes or premelanosomes were observed. Beside these tumoral cells abundant typical fibroblastic elements were found. There was a great amount of collagen fibers with periodicity superior to the normal. The conclusion is that the desmoplastic melanoma must be considered as a tumor of mesenchimatous origin intervening in its development multiple local and general factors.
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PMID:[Desmoplastic melanoma]. 34 19

The tapetum lucidum of the alligator gar Lepisosteus was shown by t.l.c. to contain a new phenolic amino acid, which is apparently a major constituent of the reflecting material. It was isolated in a yield of 0.5 mg/eye and its physical and chemical characteristics, especially reductive hydrolysis with hydriodic acid giving dopa (3,4-dihydroxyphenylalanine) and cysteine, suggested that it might to SS-dicysteinyldopa. Tyrosinase oxidation of L-dopa in the presence of an excess of L-cysteine yielded, in addition to known 5- and 2-S-cysteinyldopa, the same amino acid as that isolated from the eye of the gar, thus confirming the gross structure. The position of the two cysteine residues was established by the fact that tyrosinase oxidation of catechol and cyteine gave 3-S-cysteinylcatechol and 3,6-SS-dicysteinylcatechol. The natural amino acid is therefore formulated as 3-(2,5-SS-dicysteinyl-3,4-dihydroxyphenyl)alanine (2,5-SS-dicysteinyldopa), which may be formed by two consecutive additions of cysteine, first to dopaquinone and then to 5-S-cysteinyldopaquinone. The enzymic synthesis of 2,5-SS-dicysteinyldopa in vitro suggests that it may also be involved in the biosynthesis of phaeomelanin.
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PMID:A new amino acid, 3-(2,5-SS-dicysteinyl-3,4-dihydroxyphenyl)alanine, from the tapetum lucidum of the gar (Lepisosteidae) and its enzymic synthesis. 40 9

The effects of UVL-B and/or testosterone replacemnt therapy are compared in normal and castrated rats in order to determine whether testosterone is required for UVL-B (290-315 nm) stimulation of melanogenesis in the testosterone-dependent epidermal melanocyte system of the scrotal skin of black Long Evans rats. Testosterone is not a prerequisite for UVL-B stimulation of melanocytes as in both castrates and normal animals the melanocytes respond to UVL-B by increases in size, length and number of dendrites (dendriticness), and tyrosinase activity (intensity of Dopa reaction). Addition of testosterone to castrates does enhance the effects of UVL-B. However, UVL-B with or without testosterone cannot maintain normal melanogenesis in rats irradiated immediately after castration nor can it restore normal melanogenesis following long term castration. Bth the amount of UVL nergy/exposure and the number of exposures are important variables in stimulation of the epidermal melanocytes. Administration of a dose of UVL-B to castrates in a single exposure is ineffective, while the same overall dose spread over several exposures increases the size and dendriticness of melanocytes. Testosterone and UVL-B act synergistically in affecting melanogenesis although neither singly nor in combination are they able to fully restore normal melanogenesis.
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PMID:Testosterone and UVL-B stimulation of epidermal melanocytes in rat scrotal skin. 76 May 95

Tyrosinase has been measured in homogenates of foreskins from newborn babies. The tyrosine hydroxylation reaction is dependent upon 3,4-dihydroxyphenylalanine as a cosubstrate, and the Km for tyrosine is 0.15 mM, similar to the value observed for other mammalian tyrosinases. The mean enzyme activity for black babies (n = 169) is about two and one-fourth times that for white babies (n = 82). For white babies there is a significant correlation between age at circumcision and tyrosinase activity. For black babies this correlation becomes significant when four individuals with extremely high tyrosinase activities are omitted from the series.
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PMID:Tyrosinase activity in human skin. Influence of race and age in newborns. 80 95


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