ISSN:
1600-0757
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Melanocytes contain several substances formed by the nucleophilic addition of cysteine to dopaquinone. 5-S-Cysteinyldopa is the quantitatively dominant catecholic amino acid belonging to this group of compounds. Glutathione is the thiol most abundantly present in all cells studied, and the reactivity of the SH-group of this tripeptide with dopaquinone is about one-third that of cysteine. However, the amount of glutathionyldopa is at least two orders of magnitude less than that of cysteinyldopa in the melanocyte. A rapid metabolism of glutathionyldopa has therefore been suggested as an explanation for the above-mentioned findings. The enzyme responsible for hydrolysis of the γ-glutamyl bond of glutathione, γ-glutamyltranspeptidase, is present in the melanocyte, but in small quantities. Furthermore, S-cysteinylglycinyldopa, which is the product of hydrolysis by γ-glutamyltranspeptidase, is found in only very small amounts. These facts taken together contradict the hypothesis that S-cysteinyldopas in the melanocyte are formed from S-glutathionyldopas. The present investigation on IGR1 melanoma cells was performed by in situ derivatization of thiols with monobromobimane. Quantitation of the stable bimane adducts of cysteine and glutathione was achieved by reverse-phase high-performance liquid chromatography with fluorimetric detection. The concentration of reduced cysteine in the melanocytes was found to be a few percent of that of reduced glutathione. The quantities of 5-S-cysteinyldopa, 5-S-glutathionyldopa, cysteine, and glutathione observed in the cultured melanoma cells could best be explained by a pronounced compartmentalization of cysteine within the melanocyte, with a high cysteine concentration at the site of the dopaquinone formation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1600-0749.1988.tb00795.x
Permalink
