Tyrosinase isoenzymes in mammalian melanocytes. 2. Differential activation by alpha-melanocyte-stimulating hormone. 1993

P Valverde, and J C Garcia-Borron, and C Jimenez-Cervantes, and F Solano, and J A Lozano
Department of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, Spain.

In mouse melanoma melanocytes, alpha-melanocyte-stimulating hormone (MSH) stimulates differentiation, melanin synthesis and tyrosinase activity. However, the molecular mechanisms underlying these events have not yet been characterized. We have studied the activation of tyrosinase by MSH. Treatment of B16 melanoma cells with either theophylline, MSH, or its superpotent analog [Ahx4, DPhe7]MSH promotes a larger induction of tyrosine hydroxylase than of dopa oxidase activity in whole cell extracts. This higher activation of tyrosine hydroxylation was found not only in the melanosomal but also in the microsomal fraction; it appears to be dependent on continued transcription and translation since it can be blocked by actinomycin and cycloheximide. The tyrosinase activity of control and theophylline-treated extracts displayed several kinetic differences, including different Km values for both substrates and requirements for the cofactor L-dopa. SDS/PAGE, followed by a sensitive specific activity stain, demonstrated that melanosomes of control cells contain one lower-electrophoretic-mobility form of tyrosinase, whereas melanosomes of cells treated with either theophylline or MSH display, in addition to the lower-mobility form, a faster-migrating activity band. These tyrosinase forms are not interconvertible by proteolysis or deglycosylation. Their nature is discussed as related to the properties of the previously described low- and high-electrophoretic-mobility tyrosinases (LEMT and HEMT), as well as of the proteins encoded by the c and b loci.

UI MeSH Term Description Entries
D007527 Isoenzymes Structurally related forms of an enzyme. Each isoenzyme has the same mechanism and classification, but differs in its chemical, physical, or immunological characteristics. Alloenzyme,Allozyme,Isoenzyme,Isozyme,Isozymes,Alloenzymes,Allozymes
D007700 Kinetics The rate dynamics in chemical or physical systems.
D008543 Melanins Insoluble polymers of TYROSINE derivatives found in and causing darkness in skin (SKIN PIGMENTATION), hair, and feathers providing protection against SUNBURN induced by SUNLIGHT. CAROTENES contribute yellow and red coloration. Allomelanins,Melanin,Phaeomelanins
D008544 Melanocytes Mammalian pigment cells that produce MELANINS, pigments found mainly in the EPIDERMIS, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called MELANOSOMES. The large non-mammalian melanin-containing cells are called MELANOPHORES. Melanocyte
D008546 Melanoma, Experimental Experimentally induced tumor that produces MELANIN in animals to provide a model for studying human MELANOMA. B16 Melanoma,Melanoma, B16,Melanoma, Cloudman S91,Melanoma, Harding-Passey,Experimental Melanoma,Experimental Melanomas,Harding Passey Melanoma,Melanomas, Experimental,B16 Melanomas,Cloudman S91 Melanoma,Harding-Passey Melanoma,Melanoma, Harding Passey,Melanomas, B16,S91 Melanoma, Cloudman
D008861 Microsomes Artifactual vesicles formed from the endoplasmic reticulum when cells are disrupted. They are isolated by differential centrifugation and are composed of three structural features: rough vesicles, smooth vesicles, and ribosomes. Numerous enzyme activities are associated with the microsomal fraction. (Glick, Glossary of Biochemistry and Molecular Biology, 1990; from Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed) Microsome
D009074 Melanocyte-Stimulating Hormones Peptides with the ability to stimulate pigmented cells MELANOCYTES in mammals and MELANOPHORES in lower vertebrates. By stimulating the synthesis and distribution of MELANIN in these pigmented cells, they increase coloration of skin and other tissue. MSHs, derived from pro-opiomelanocortin (POMC), are produced by MELANOTROPHS in the INTERMEDIATE LOBE OF PITUITARY; CORTICOTROPHS in the ANTERIOR LOBE OF PITUITARY, and the hypothalamic neurons in the ARCUATE NUCLEUS OF HYPOTHALAMUS. MSH,Melanocyte Stimulating Hormone,Melanocyte-Stimulating Hormone,Melanophore Stimulating Hormone,Melanotropin,MSH (Melanocyte-Stimulating Hormones),Melanophore-Stimulating Hormone,Hormone, Melanocyte Stimulating,Hormone, Melanocyte-Stimulating,Hormone, Melanophore Stimulating,Melanocyte Stimulating Hormones,Stimulating Hormone, Melanocyte,Stimulating Hormone, Melanophore
D004591 Electrophoresis, Polyacrylamide Gel Electrophoresis in which a polyacrylamide gel is used as the diffusion medium. Polyacrylamide Gel Electrophoresis,SDS-PAGE,Sodium Dodecyl Sulfate-PAGE,Gel Electrophoresis, Polyacrylamide,SDS PAGE,Sodium Dodecyl Sulfate PAGE,Sodium Dodecyl Sulfate-PAGEs
D004789 Enzyme Activation Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1, activation by ions (activators); 2, activation by cofactors (coenzymes); and 3, conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme. Activation, Enzyme,Activations, Enzyme,Enzyme Activations
D004790 Enzyme Induction An increase in the rate of synthesis of an enzyme due to the presence of an inducer which acts to derepress the gene responsible for enzyme synthesis. Induction, Enzyme

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