The N-glycans of membrane glycoproteins are mainly exposed to the extracellular space. Human tyrosinase is a transmembrane glycoprotein with six or seven bulky N-glycans exposed towards the lumen of subcellular organelles. The central active site region of human tyrosinase is modeled here within less than 2.5 Å accuracy starting from Streptomyces castaneoglobisporus tyrosinase. The model accoun...

THE work of a number of investigators has shown the presence of tyrosinase in various species of Macrolepidoptera, but it is not clear from the literature whether the occurrence of tyrosinase is exceptional or general. A survey has therefore been made of some widely representative species, comprising four Rhopalocera (butterflies) and 25 Heterocera (moths). Since most tyrosinase is usually foun...

The activity of tyrosinase (EC 1.10.3,1 o-diphenol:02 oxidoreductase) was found to be in melanosomes, smooth-surface membranes, rough-surface membranes , and ribosomes when they are isolated from Harding-Passey mouse mela-noma. In vivo incorporation studies of 14C-dopa into these cell particles were carried out in order to clarify the site of malanin formation in melanocytes. '4C-dopa incorpora...

Tyrosinase is a copper-containing enzyme that regulates melanin biosynthesis in mammals. Mutations at a single N-glycosylation sequon of tyrosinase have been reported to be responsible for oculocutaneous albinism type IA in humans, characterized by inactive tyrosinase and the total absence of pigmentation. To probe the role that each N-glycosylation site plays in the synthesis of biologically a...

Pigmentation in mammals is under complex genetic control. Amongst the genes involved in this process, those encoding tyrosinase and the tyrosinase-related-proteins 1 and 2 have been well characterized and share a number of features. Recently, the murine tyrosinase-related-protein-2 gene was shown to encode dopachrome-tautomerase activity and was mapped to the slaty locus. Human tyrosinase and t...

The production of pigment in mammalian melanocytes requires the contribution of at least three melanogenic enzymes, tyrosinase and two other accessory enzymes called the tyrosinase-related proteins (Trp1 and Trp2), which regulate the type and amount of melanin. The last two proteins are paralogues to tyrosinase, and they appeared late in evolution by triplication of the tyrosinase gene. Tyrosin...

Arbutin, a naturally occurring beta-D-glucopyranoside of hydroquinone, is effective in the topical treatment of various cutaneous hyperpigmentations characterized by hyperactive melanocyte function. We examined the mechanism of its depigmenting action in human melanocyte cultures. Arbutin inhibited the tyrosinase activity of cultured human melanocytes at noncytotoxic concentrations. It did not ...

Herbal nanoparticles gain lot of attention because of their pharmaceutical importance. The present study reports the eco-friendly synthesis, characterization and their tyrosinase activity of silver nanoparticles (AgNPs) using aqueous extract of Bidens frondosa. The appearance of brown color indicated the formation of B. frondosa AgNPs. The Formation of AgNPs was confirmed by UV–Vis spectroscopy...

1. pH stability diagrams for protyrosinase and for tyrosinase were constructed. 2. Above pH 7.30 protyrosinase is unstable. Between pH 7.30 and pH 9.30 there is a partial destruction. Beyond pH 9.30 it changes irreversibly into tyrosinase which in turn is destroyed beyond pH 10.12. 3. Through the lower ranges of pH protyrosinase is less stable than tyrosinase The former is destroyed below pH 4....

Tyrosinase activity was demonstrated in the sera from melanoma-bearing mice. One, two, and three weeks following tumor transplantation, 12, 80, and 90% of the respective sera from these mice showed positive results. No sera from normal mice had tyrosinase activity. There was a correlation between tumor size and tyrosinase activity, the coefficient of correlation being 0.71. The activity in the ...