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H Rorsman

Publications and source records attributed to H Rorsman.

At least 55 records · Page 3Linked to original sources
PubMed1986

Oxidation of dopa in the skin of black and albino mice.

The dopa oxidase activity of tyrosinase in the skin from albino and black mice was assayed using a technique based on the formation of two diastereomers of 5-S-cysteinyldopa when incubating tissue extracts with both L-dopa and D-dopa as substrates in the presence of cysteine. The amounts of 5-S-L-cysteinyl-L-dopa and 5-S-L-cysteinyl-D-dopa formed were then determined. In the extract from black mouse skin the L-L-diastereomer was produced in more than ten times the amount of the L-D-diastereomer. This stereospecific dopa-oxidation is indicative of the presence of tyrosinase and corresponds well with earlier determinations of the rates of oxidation for human tyrosinase, using L-dopa and D-dopa as substrates. Stereospecific dopa oxidation was absent in albino skin, and the nonspecific dopa-oxidation was two orders of magnitude less than the dopa oxidation in black skin. The study demonstrates the lack of tyrosinase activity in albino skin, and quantifies the non-specific dopa oxidation. The lack of tyrosinase activity in the eluates from albinotic skin was found not to be due to the presence of a tyrosinase inhibitor.

Albinism↗
PubMed1986

Trichochromuria in melanosis of melanoma.

Two patients with metastasizing melanoma and diffuse melanosis have previously been reported to excrete large quantities of trichochromes in the urine. The present study describes 2 further melanoma patients with diffuse melanosis and trichochromuria. The hair of one of the patients which had been red in childhood and turned brown in adult age returned to red with the appearance of melanosis. Normal excretion of a methylated melanocytic metabolite, 6-hydroxy-5-methoxyindole-2-carboxylic acid, was observed in this patient, possibly indicating exhaustion of the methylating system. The other patients excreted large quantities of 6-hydroxy-5-methoxyindole-2-carboxylic acid. Both patients showed highly increased excretion of 5-S-cysteinyldopa. Both patients with melanosis exhibited fine electrone-dense granules in lysosomes of dermal histiocytes. The findings support the concept that trichochromes or similar pigments in dermal histiocytes are responsible for diffuse melanosis in melanoma patients.

Adult↗
PubMed1986

Metabolism of 5-S-glutathionyldopa.

5-S-Glutathionyldopa is oxidized at incubation with tyrosinase and dopa producing a black pigment. The reaction proceeds with the formation of two chromophores with absorption spectra similar to those of dopachrome and melanochrome, respectively. Zn2+ catalyses the formation of the melanochrome-like compound. The oxidation of 5-S-glutathionyldopa by dopaquinone, formed by the action of human tyrosinase and mushroom tyrosinase, is considerably slower than that of 5-S-cysteinyldopa. The higher oxidation potential of 5-S-glutathionyldopa, and/or the greater number of dopaquinone molecules necessary for pigment formation from 5-S-glutathionyldopa and/or the formation of tyrosinase-inhibiting products from 5-S-glutathionyldopa can explain the slower oxidation of this compound. The oxidative pathways suggested for 5-S-glutathionyldopa by the present findings may be relevant both in the melanocyte and in non-specific oxidation of cathechols occurring in other cells.

Basidiomycota↗
PubMed1985

Production of 6-hydroxydopa by human tyrosinase.

A tyrosinase obtained from cultured human melanoma cells was found to oxygenate 2,4-dihydroxyphenylalanine to the strongly cytotoxic amino acid 6-hydroxydopa (2,4,5-trihydroxyphenylalanine). The oxygenation was dependent on the presence of a reducing co-substrate such as dopa or dopamine. The rate of oxygenation of 2,4-dihydroxyphenyl-D,L-alanine was similar to that of L-tyrosine, the normal substrate of tyrosinase. The enzymatic reaction demonstrated may prove of value in the chemotherapy of human melanoma.

Catalysis↗
PubMed1985

Melanocyte metabolites in the urine of people of different skin colour.

The urinary excretion of 2 melanocyte metabolites was studied in normal people of different skin type. The sulphur-free indole derivative 6-hydroxy-5-methoxyindole-2-carboxylic acid was excreted in larger quantities by people with genetically dark skin, whereas the excretion of 5-S-cysteinyldopa was not related to pigment type. No correlation between 5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid excretion emerged.

Adult↗
PubMed1985

Oxidation of dopa in human albinism.

The urine of an albino woman contained small quantities of 5-S-cysteinyldopa; 6-hydroxy-5-methoxyindole-2-carboxylic acid, a melanin precursor metabolite, was lacking. The 5-S-cysteinyldopa excretion observed may reflect non-specific oxidation of dopa. Two other albino patients showed normal values for the excretion of 5-S-cysteinyldopa and of 6-hydroxy-5-methoxyindole-2-carboxylic acid.

Adult↗
PubMed1985

Urinary excretion of 5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid: differences between pigmented and albino mice.

Urinary excretion of the phaeomelanin precursor 5-S-cysteinyldopa (5-S-CD) and the eumelanin metabolite 6-hydroxy-5-methoxyindole-2-carboxylic acid (6H5MI-2-C) was studied in black and albino mice. The urinary concentration of 5-S-CD was 31.7 ng/ml in black and 16.1 ng/ml in albino mice. The concentration of 6H5MI-2-C was 21.0 ng/ml in the urine of black mice. The compound could not be demonstrated in the urine of albino mice.

Albinism↗
PubMed1985

Urinary excretion of melanocytic metabolites in fertile women.

Pregnant women and women taking oral contraceptives show urinary excretion values of 5-S-cysteinyldopa and of 6-hydroxy-5-methoxyindole-2-carboxylic acid in the same range as nonpregnant women not taking oral contraceptives. The excretion of these melanoma markers can therefore be used in in the biochemical diagnosis of metastatic melanoma in pregnancy and in women taking oral contraceptives.

Adult↗
PubMed1984

Inactivation of human tyrosinase by cysteine. Protection by dopa and tyrosine.

Human tyrosinase prepared from cultured melanoma cells is inactivated by 10 mM cysteine. The inactivation of the enzyme by cysteine is less pronounced in the presence of catalase and superoxide dismutase. Thus, oxygen radicals and/or hydrogen peroxide may contribute to the inactivation of human tyrosinase by cysteine. Dopa and/or tyrosine protects tyrosinase against inactivation by cysteine. The protection observed with tyrosine alone indicates that oxidation of substrate is not necessary for the protection. The effect of dopa and/or tyrosine is probably due to steric hindrance at the active site preventing the access of cysteine to the copper.

Catalase↗
PubMed1983

An estimate of the melanocyte mass in humans.

The size of the melanocyte system in humans was estimated as though all active melanocytes in the body were assembled in a single compact organ. Our estimates indicate that the epidermal melanocytes constitute the dominant part of the "melanocyte organ." In an adult human not recently exposed to sunlight, the functionally active epidermal melanocytes form a tissue 1.0-1.5 cm3. Other melanocytes, such as those in the mucous membranes, the follicles, and the eyes, constitute only a small proportion of the total melanocyte cell mass.

Body Composition↗
PubMed1983

Methaemoglobin-catalysed formation of dopa and 6-OH-dopa from tyrosine.

An extract of bovine retina and choroid with tyrosine hydroxylating and dopa-oxidizing capacity also showed marked formation of 6-OH-dopa on incubation with tyrosine and ascorbic acid. The extract contained appreciable amounts of methaemoglobin as determined spectrophotometrically, and boiled extracts also showed catalytic activity. The effect of methaemoglobin on the oxidation of tyrosine and dopa was therefore investigated. Methaemoglobin catalysed the formation of dopa and 6-OH-dopa in the presence of tyrosine and ascorbic acid. Hydrogen peroxide plays an important role in this reaction: the rates of formation of both dopa and 6-OH-dopa were increased by addition of hydrogen peroxide but diminished by addition of catalase. Methaemoglobin also catalysed the formation of cysteinyldopa from dopa and cysteine.

Animals↗
PubMed1983

5-S-cysteinyldopa and pigment response to UVA light.

5-S-Cysteinyldopa concentrations in serum were studied in healthy individuals exposed to daily high-intensity UVA radiation. A marked increase in 5-S-cysteinyldopa was found after 3 days, and in some individuals concentrations were still higher after 7 to 10 days. The immediate pigment darkening (IPD) and delayed tanning (DT) were weak or absent at pressure sites, i.e. in skin with a low concentration of oxygen.

Adult↗
PubMed1983

Diastereomers of 5-S-cysteinyldopa.

Diastereomers of 5-S-cysteinyldopa formed from D-dopa and L-cysteine or from L-dopa and D-cysteine can be separated from 5-S-cysteinyldopa formed from L-dopa and L-cysteine by liquid chromatography. The diastereomers have a great potential as internal standards in the analysis of 5-S-cysteinyldopa. They can be used as reference substances in the differentiation of stereospecific enzymatic oxidation of dopa from non-specific oxidation.

Chromatography, Liquid↗
PubMed1983

Tyrosinase activity in the medium of human melanoma cell cultures.

The medium of cultured melanoma cells was studied for tyrosine hydroxylation and dopa-oxidizing activity. The supernatant obtained after centrifugation at 100 000 g for 2 hours was treated with ammonium sulphate, and the precipitate obtained between 35 and 50% saturation was used. Dopa was determined as the product of tyrosine hydroxylation and 5-S-cysteinyldopa as the product of dopa oxidase activity. Determinations were performed with HPLC and electrochemical detection. Our preparation of culture medium of cells showed the following. 1) No hydroxylation of tyrosine in the absence of co-factor. 2) Hydroxylation of L-tyrosine in the presence of dopamine. No hydroxylation with boiled medium. Minimal effect of catalase on hydroxylation. 3) Hydroxylation of tyrosine in the presence of ascorbic acid. Hydroxylation was catalyzed also with boiled medium. Catalase strikingly diminished hydroxylation. 4) Oxidation of L-dopa to dopaquinone determined as its main reaction product with cysteine, 5-S-cysteinyl-dopa. There was negligible oxidation with boiled medium. 5) With dopamine as co-factor the catalysis of tyrosine hydroxylation was stereospecific for L-tyrosine. Dopa oxidase activity was also stereospecific for L-dopa.

Ascorbic Acid↗
PubMed1983

The effect of catalase on the inactivation of tyrosinase by ascorbic acid and by cysteine or glutathione.

When tyrosine was incubated with tyrosinase in the presence of ascorbic acid, dopa and 5-hydroxydopa were formed and the enzyme was inactivated. In the presence of catalase, more dopa and 5-hydroxydopa were formed because enzyme inactivation was prevented. Incubation of dopa and cysteine with small amounts of mushroom tyrosinase led to rapid inactivation of the enzyme. This inactivation was accelerated in the presence of catalase. New systems developed have been useful in demonstrating the role of hydrogen peroxide in tyrosinase inactivation by several compounds of importance in melanin biochemistry. Cysteine and glutathione inactivated tyrosinase. Addition of catalase increased the inactivation at high thiol concentrations, but decreased the inactivation at low concentrations. Ascorbic acid and 5-hydroxydopamine also inactivated tyrosinase, but with these compounds inactivation was completely prevented by addition of catalase. The inactivation by dopamine was negligible under the experimental conditions. Inactivation of tyrosinase by ascorbic acid and by 5-OH-dopamine was found dependent on oxygen, whereas inactivation by cysteine and glutathione was independent of oxygen. Large amounts of serum albumin protected tyrosinase from inactivation by ascorbic acid and 5-OH-dopamine, but did not prevent inactivation by cysteine and glutathione. The presence of substrate had a protective effect on the inactivation of tyrosinase by cysteine.

Ascorbic Acid↗
PubMed1983

Dopa oxidation and tyrosine oxygenation by human melanoma tyrosinase.

A tyrosinase purified from cultured human melanoma cells was studied for dopa oxidation and tyrosine oxygenation. Km for oxidation of L-dopa was 0.5 mM, and for D-dopa 3 mM. L-tyrosine was oxygenated only in the presence of a cosubstrate. L-Dopa was superior to D-dopa, dopamine, L- and D-alpha-methyldopa, dopac, and 5,6-dihydroxyindole-2-carboxylic acid as cosubstrate. Ascorbic acid, 5-S-cysteinyldopa, and 5-OH-dopa did not function as cosubstrates. The rate of tyrosine hydroxylation was much lower than that of dopa oxidation. Tyrosine inhibits dopa oxidation, and dopa in high concentrations inhibits tyrosine hydroxylation. The cosubstrate function of dopa, the substrate functions of dopa and tyrosine, and the mutual inhibition of tyrosinase by these compounds are explained in three equations.

Catechol Oxidase↗
PubMed1982

The effect of cysteine on oxidation of tyrosine, dopa, and cysteinyldopas.

The influence of cysteine on the oxidation of tyrosine, dopa, and monocysteinyldopas by mushroom tyrosinase was reexamined. During oxidation of tyrosine in the presence of cysteine the concentration of dopa increased slowly, whereas the concentration of cysteinyldopas increased more rapidly. When the concentration of cysteine decreased the cysteinyldopas were rapidly consumed and dopa concentrations increased sharply. Experiments on the oxidation of dopa by tyrosinase in the presence of cysteine showed that this thiol does not inhibit the oxidation. Dopa concentrations decreased more rapidly in the presence of cysteine because cysteine addition to dopaquinone prevented reformation of dopa from dopaquinone. Both 2-S-cysteinyldopa and 5-S-cysteinyldopa are substrates for tyrosinase. The oxidation of cysteinyldopas was inhibited at high cysteine concentrations. The greater part of 2,5-S,S-dicysteinyldopa formed during the oxidation of monocysteinyldopas in the presence of cysteine is derived from 5-S-cysteinyldopa, which is a better substrate for tyrosinase than 2-S-cysteinyldopa. The fact that cysteine binds more rapidly to 5-S-cysteinyldopaquinone than to 2-S-cysteinyldopaquinone further stresses the importance of 5-S-cysteinyldopa in the formation of 2,5-S,S-dicysteinyldopa. Oxidation of dopa in the presence of cysteine and glutathione or methionine showed that glutathione is added to dopaquinone but less rapidly than cysteine. Methionine showed insignificant addition to dopaquinone. When dopa or 5-OH-dopa is added to an incubate of cysteinyldopa and tyrosinase the oxidation of cysteinyldopa is accelerated owing to oxidation of cysteinyldopa by dopaquinone or 5-OH-dopaquinone.

Ascorbic Acid↗