Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A rate of the tyrosine hydroxylase reaction was estimated by an increase in absorption at 335 nm, which was caused by oxidation of pterin cofactor 6,7-dimethyl-5, 6, 7, 8-tetrahydroxypterin (DMPH) coupled with the convertion of the substrate 1-tyrosine into dihydroxyphenylalanine. At pH 6.2 the ratios of molar extinction were as follows: in trisacetate ADMPH4-1370, ADMPH2-5350; in tris-malate tadmph4-1250, admph25300. the enzyme, associated with membranes, had the Km value for Tyr-0.045 mM, the Km for DMPH4 was 0.18 mM; the soluble enzyme had Km for Tyr-0,050 mM, the Km for DMPH4 was 0.74 mM. The stoichiometry of the reaction was 1:1 (I mole DOPA per I mole of DMPH2 formed).
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PMID:[Method for the direct spectrophotometric determination of the rate of the tyrosine hydroxylase reaction]. 1 96

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

Pigment freckles seen in donor and recipient sites at intermediate skin grafting were studied, chiefly by means of Falck & Hillarp's fluorescence method, with the following results. (1) An important role is played by the regenerative eccrine sweat ducts in the mechanism of recurrence of so-called "lentigines" after incomplete removal. (2) Junctional activity, not associated with the regeneration of epidermal appendages, can recommence in the epidermis of intradermal nevi. (3) B-type nevus cells once again actively produce melanin. (4) Specific fluorescence was observed corresponding to the melanin granules distributed in the manner of "nuclear caps" in keratinocytes around junctional activities. This latter finding may indicate that melanosomes which still contain DOPA are transferred from melanin-producing cells to keratinocytes.
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PMID:Pigmented nevus divided between recipient and donor sites by intermediate skin grafting procedure: a study with fluorescence method (Falck & Hillarp). 7 37

The morphological substrates of pigmented and depigmented skin as well as the structural characteristics of spontaneously developing melanomas were revealed by clinical, light- and electron microscopic methods in gray horses (Lipizzaner breed) from the Vienna Spanish Riding School. On clinical investigations in a group of 31 older horses (more than 10 years old) 20 exhibited melanomas, whereas 23 younger animals (less than 10 years of age) had no evidence for visuable melanotic tumors. Concomitantly with the progressive graying of the hair a depigmentation of the skin was frequently observed. Light and electron microscopic studies of skin biopsies revealed that in pigmented areas melanin is produced by DOPA-positive melanocytes and stored in form of large single melanosomes within keratinocytes. In depigmented areas melanocytes and melanosomes are completely lacking, but a high number of indeterminated cells is present in the basal layer. Melanotic tumors from the root of the tail, the lips, the perianal region, the sholder and intestinal lymph nodes exhibited either encapsulated nodules or diffusely infiltrating melanomatous structures similar to blue nevi in the dermis. Junctional activity could never be observed. A differentiation between melanin-producing tumor cells and melanophages was difficult in light microscopy but possible according to ultrastructural characteristics.
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PMID:[Comparative investigations of depigmented and melanomatous lesions in gray horses of the lipizzaner breed (author's transl)]. 90 Sep 91

Junction nevus, dermal nevus, melanosis circumscripta praecancerosa Dubreuilh, superficial spreading melanoma, and nodular melanoma were investigated and characterized by use of the formalin induced fluorescence method (FIF). In the vicinity of junctional nevus cell clusters and near tumor cells of the superficial spreading melanoma increased numbers of melanocytes are found. These show different types of dendritic branching. Spherical nevus cells however are completely devoid of dendritic processes. On the other hand, the atypical pigment cells in melanosis circumscripta praecancerosa Dubreuilh exhibit a shape similar to that of melanocytes, whereas the globular cells of superficial spreading melanoma have the appearance of nevus cells. The arrangement of nodular melanoma cells resembles that observed in dermal nevus. However the characteristic decrease in fluorescence intensity from epidermal junction to deeper dermis as observed in the dermal nevus was missed in nodular melanomas. Dendritic pigment cells displaying formalin induced fluorescence (FIF) could be demonstrated in all types of malignant melanomas investigated in the present study. The fluorophores of the pigment lesions are characterized microspectrofluorimetrically by (1) ill-defined emission maxima between 470 and 490 nm and (2) a clear-cut excitation maximum at 430 nm accompanied by a lower one at 320 nm. Hydrochloric acid vapor induces a hyposochromic shift of the 430 nm excitation maximum to 370-380 nm and a marked elevation of the 320 nm maximum. These results indicate fluorophores of DOPA and its derivatives; in this respect there are no marked differences between melanocytes, nevus cells and the cells of malignant melanoma.
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PMID:[Fluorescence histochemical and microfluorometrical investigations of pigmentary tumors of the skin (author's transl)]. 119 Aug 35

We investigated a 4-year-old Japanese boy with oculocutaneous albinism who had a solitary pigmented mole measuring 5 mm in diameter on his back. An electron microscopic tyrosine incubation test and a DOPA reaction test clearly demonstrated the presence of tyrosinase activity in the patient's hypopigmented skin. The presence of tyrosinase activity was confirmed by tests on hair bulb samples. Histopathological evidence showed that the mole was a typical compound cellular naevus with melanin pigmentation. Although no reports to date have focused on the relationship between pigmented naevi in albinism and tyrosinase activity, our findings suggest that the occurrence of pigmented naevi in an albino may indicate the presence of tyrosinase activity.
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PMID:Do pigmented naevi in albinism provide evidence of tyrosinase positivity? 147 26

The phase equilibria, hydration, and sodium counterion association for the systems DOPA-2H2O, DOPS-2H2O, DOPG-2H2O, and DPG-2H2O were investigated with 2H, 23Na, and 31P NMR and X-ray diffraction. The following one-phase regions were found in the DOPA-water system: a reversed hexagonal liquid-crystalline (HII) phase up to about 35 wt % water and a lamellar liquid-crystalline (L alpha) phase between about 55 and 98 wt % water. The area per DOPA molecule was 36-65 A2 in the HII phase (10-40 wt % water) and 69 A2 in the L alpha phase (60 wt % water). DOPS and DOPG with 10-98 wt % water, and DPG with 20-95 wt % water formed an L alpha phase at temperatures between 25 and 55 degrees C. At temperatures above 55 degrees C, DPG with 20 and 30 wt % water formed a mixture of L alpha, HII, and cubic liquid-crystalline phases, the mole percent of lipid forming nonlamellar phases being smaller at 30 wt % water than at 20 wt % water. DPG with 10 wt % water probably formed a mixture of an L alpha phase and at least one nonlamellar liquid-crystalline phase at 25 and 35 degrees C, and a pure HII phase at 45 degrees C and higher temperatures. At water concentrations above about 50 wt % the 23Na quadrupole splitting was constant for all four lipid-water systems studied, implying that the counterion association to the charged lipid aggregates did not change upon dilution. These experimental observations can be described with an ion condensation model but not with a simple equilibrium model. The fraction of counterions located close to the lipid-water interface was calculated to be greater than 95%. The 2H and 23Na NMR quadrupole splittings of 2H2O and sodium counterions, respectively, indicate that the molecular order in the polar head-group region decreases for the L alpha phase in the order DOPA approximately DPG greater than DOPS greater than DOPG.
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PMID:Effect of head-group structure and counterion condensation on phase equilibria in anionic phospholipid-water systems studied by 2H, 23Na, and 31P NMR and X-ray diffraction. 193 19

In order to look for a new culture system suitable for investigating on melanocyte biology, in-vitro experiments have been carried out on pigmented basal cell carcinoma, pigmented seborrhoeic keratosis and melanocytic nevus. Melanocytes cultured from pigmented basal cell carcinoma and pigmented seborrheic keratosis are dendritic and DOPA positive. These cells can be considered similar to those of normal skin. Pigmented cells cultured from nevi are quite different. They are spindle-shaped and only to a little extent are DOPA positive. These findings suggest that nevus cells could be non mature melanocytes stopped at an intermediate stage of differentiation.
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PMID:[Differences in the culture of pigment cells from various sources]. 632 29

A patient with Parkinson's disease developed a malignant melanoma within a congenital nevus after starting levodopa therapy. Levodopa has a central role in the metabolism of the melanocyte but data do not permit the conclusion that it promotes the development of malignant melanoma. However, patients receiving levodopa should be monitored for skin changes suggestive of melanoma.
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PMID:Malignant melanoma and levodopa. 674 49

Until recently little was known concerning the chemical details of the mechanism of interaction of flavin-linked mitochondrial membrane bound monoamine oxidase (MAO) with its substrates and inhibitors. Substrates which have enzymes as their targets have been valuable in elucidating active site residues and structural features. Acetylenic amines as exemplified by clorgyline, deprenyl and pargyline are called 'suicide inhibitors' because an irreversible inhibitor is formed by the action of MAO from a relatively innocuous compound which acts as a substrate. These inhibitors can selectively inactivate MAO 'type A' and/or 'type B'. MAO isolated in homogeneous form from liver or kidney contains 1 mole of covalently bound coenzyme, cysteinyl-flavin, per mole enzyme. The flavin is bound to a pentapeptide via the thio-ether of cysteine at the 8 alpha-position of the isoalloxazine. A comparison of the inhibitory effects of clorgyline, deprenyl and pargyline on liver enzyme preparations from bovine or rat have confirmed our expectation that these irreversible inactivators form the same type of adduct with the cysteinyl-flavin active site of MAO 'type A' and 'type B', and that binding is stoichiometric at the N-5 of the covalently bound flavin in a flavocyanine linkage. Substrates protect from inhibition. In contrast to the reported observation of Tipton (39), pig brain mitochondrial MAO purified by two alternative methods contains cysteinyl-flavin in substantial amounts. The turnover number of enzyme from brain per mole of cysterinyl-flavin in apparently homogeneous samples is nearly the same as that of highly purified kidney and liver enzyme. Thus it is apparent that brain MAO also contains cysteinyl-flavin at the active center and therefore it is expected that acetylenic as well as hydrazine inhibitors form the same linkage with the flavin moiety as that formed with enzyme from peripheral tissues. A specific inhibitor for the deamination and potentiation of dopamine formed in the brain of Parkinsonian patients after treatment with L-Dopa has been regarded desirable. Deprenyl, a selective MAO 'type B inhibitor without the 'cheese effect', is the most potent inactivator of human brain MAO, and clinical results show that the drug is very useful in the treatment of Parkinson's disease and depression.
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PMID:Biochemical characterization of the active site of brain monoamine oxidase. 678 74


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