tyrosinase (ec: 1.14.18.1) is a copper - containing enzyme which is distributed in all domains of life such as prokaryote, eukaryote, mammals, invertebrates and plants. tyrosinase catalyzes the oxidation of monophenols to diphenols and diphenols to o-quinones . the tyrosinase crystallographic data shows two histidine -rich regions named cua and cub. a loop containing residues m374, s375 and v37...

Tyrosinase (EC 1.14.18.1) is a copper-containing metalloglycoprotein that catalyzes several steps in the melanin pigment biosynthetic pathway; the hydroxylation of tyrosine to L-3,4-dihydroxyphenylalanine (dopa) and the subsequent oxidation of dopa to dopaquinone. It has been proposed that tyrosinase is also able to oxidize 5,6-dihydroxyindole (DHI), a later product in the melanogenic pathway, ...

Tyrosine hydroxylase, dopa oxidase, and peroxidase activities were studied in soluble fractions of B16 melanoma tumor homogenates by polyacrylamide gel disc electrophoresis. Stained gels were scanned photometrically and gel slices were assayed radiometrically. In these preparations, the two bands of tyrosine hydroxylating activity were completely separated from the peroxidase activity but coinc...

A variant of the Cloudman 5-91 melanoma is described which is characterized by a low level of tyrosinase and dopa oxidase (phenolase complex) activity. On the ultrastructural level this is expressed by a preponderance of melanosomes (im mature melanin granules) rather than mature melanin particles. Extracts of the tumor exhibit only dopa oxidase activity. With tumor slices, tyrosinase activity ...

1. L-DOPA was administered to rats by twice daily intraperitoneal injection for a period of eleven days. The daily dose was gradually increased from 250 mg/kg to 1 g/kg. The animals were killed 12 h after the last injection and tissue catechol-O-methyl transferase, DOPA-decarboxylase and monoamine oxidase activity determined.2. Catechol-O-methyl transferase activity was reduced in the liver (46...

Animal peroxidases are iron-containing proteins that catalyze the oxidation of a variety of substances by hydrogen peroxide. Histochemically, the myeloperoxidase of granulocytes is the most easily detected (1). Tyrosinase (dopa oxidase) is a copper-containing enzyme complex capable of converting both tyrosine to dopa (slowly) and dopa to dopa quinone (rapidly) in the melanin synthetic pathway (...

The histopathological diagnosis of melanomas with no demonstrable pigment is difficult. Such tumors are to be differentiated from anaplastic carcinomas, especially of the squamous and adeno types, and from sarcomas showing marked anaplasia or spindle cells. In a previous report from this laboratory (1), a colorimetric method for determination of L-3,4-dihydroxyphenylalanine (dopa) oxidase activ...

Mammalian tyrosinase as currently defined has two catalytic functions: 1) the oxidation of tyrosine to L-3,4-dihydroxyphenylalanine (dopa) and 2) the oxidation of dopa to dopa quinone (1-9). Although an imposing body of evidence has been advanced in support of this interpretation, Okun and associates have recently challenged the prevailing concept of the action of tyrosinase ( 10, 11 ). They ha...

polyphenol oxidase (ppo) from tomatoes was extracted and partially purified through  (nh4)2so4 precipitation, dialysis and ion exchange chromatography. the activity of polyphenol oxidase was investigated in solanum lycopersicum. spectrophotometric method was used to assay the enzyme activity and the kinetic constants - maximum enzyme velocity (vmax) and michealis - menten constant (km). of the ...

Polyphenol oxidase (PPO) from tomatoes was extracted and partially purified through  (NH4)2SO4 precipitation, dialysis and ion exchange chromatography. The activity of polyphenol oxidase was investigated in solanum lycopersicum. Spectrophotometric method was used to assay the enzyme activity and the kinetic constants - maximum enzyme velocity (Vmax) and Michealis - Menten constant (Km). Of the ...