Publication: The melanogenic system of the liver pigmented macrophages of Rana esculenta L. - Tyrosinase activity
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Date
2007
Authors
Gallone, A. ; Sagliano, A. ; Guida, G. ; Ito, S. ; Wakamatsu, K. ; Capozzi, V. ; Perna, G. ; Zanna, P. ; Cicero, R.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The enzyme system responsible for
Amphibian Kupffer Cell (KC) melanogenesis has not
been entirely elucidated. This research demonstrates that
the KC melanosomes of Rana esculenta L. possess a
tyrosine-hydroxylase (TH) activity, showing that a
tyrosinase is the enzyme involved in the melanogenesis.
The TH reaction depends on catalytic Dopa as a cofactor
and is not affected by catalase or H2O2, showing that it is
catalysed by the tyrosinase and not by the peroxidase
present in the melanosomes.
The TH reaction is activated by Cu2+ ions but not by
other tyrosinase activators such as limited proteolysis,
protein ageing, and Sodium Dodecyl Sulphate (SDS).
SDS inhibited the KC TH activity even below the
critical micelle concentration. All these results suggest
that the KC-tyrosinase differs in structure from other
known tyrosinases.
Using anti-KC-tyrosinase antobodies, we observed
that the sites of the tyrosinase location within the cell are
the same as those described in the melanocytes. In the
immunoblots, the anti-KC-tyrosinase antibodies also
recognised two protein bands, at the higher molecular
weight ranges, in the protein electrophoretic pattern.
Moreover, the tyrosinase activity was limited to the
highest molecular weight band of about 260 kDa,
suggesting that the enzyme activity could depend on a
molecular aggregate. The melanin produced in the liver was found to be a 5,6-dihydroxyindole-rich eumelanin
similar to the Sepia melanin.
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