Document Detail

De novo sulfation of L-tyrosine in HepG2 human hepatoma cells and its possible functional implication.
MedLine Citation:
PMID:  8001547     Owner:  NLM     Status:  MEDLINE    
HepG2 human hepatoma cells, labeled with [35S]sulfate in the presence of 10-30 micrograms/ml of cycloheximide, released up to 64% of the amount of free tyrosine-O-[35S]sulfate produced and released by cells labeled in the absence of cycloheximide. A time-course study revealed that, in cells incubated in medium containing [3H]tyrosine, free [3H]tyrosine-O-sulfate was produced within 5 min of incubation, whereas no [3H]tyrosine-sulfated proteins were detected until 20 min after the incubation had begun. Using 3'-phosphoadenosine, 5'-phospho[35S]sulfate as the sulfate donor, HepG2 cell homogenate was shown to contain enzymic activity catalyzing the sulfation of L-tyrosine with the formation of tyrosine-O-[35S]sulfate. Upon subcellular fractionation, the majority of the enzyme activity was found in the cytosolic fraction. The enzyme, designated tyrosine sulfotransferase, displayed the optimum activity at pH 8.0 in the presence of 10 mM Mn2+. Under optimum conditions, the apparent Km of the enzyme for L-tyrosine, at 4.5-microM concentration of 3'-phosphoadenosine, 5'-phosphosulfate, was determined to be 1.95 mM, while that for 3'-phosphoadenosine, 5'-phosphosulfate, at 1 mM L-tyrosine concentration, was 8.3 microM. The Vmax determined under these conditions was 1.05 protein-1. A tyrosine-dependence study showed that, for cells labeled with [35S]sulfate, the production and release of free tyrosine-O-[35S]sulfate appeared to proceed actively and increase proportionally to the L-tyrosine concentration when it was raised above a threshold level in the culture medium. These results may imply a possible involvement of sulfation in removing excess intracellular L-tyrosine.
Y Sakakibara; M Suiko; M C Liu
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  European journal of biochemistry / FEBS     Volume:  226     ISSN:  0014-2956     ISO Abbreviation:  Eur. J. Biochem.     Publication Date:  1994 Dec 
Date Detail:
Created Date:  1995-01-26     Completed Date:  1995-01-26     Revised Date:  2007-07-23    
Medline Journal Info:
Nlm Unique ID:  0107600     Medline TA:  Eur J Biochem     Country:  GERMANY    
Other Details:
Languages:  eng     Pagination:  293-301     Citation Subset:  IM    
Department of Biochemistry, University of Texas Health Center at Tyler 75710.
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MeSH Terms
Carcinoma, Hepatocellular / enzymology*
Cell Fractionation
Cycloheximide / pharmacology
Cytosol / enzymology
Hydrogen-Ion Concentration
Liver Neoplasms / enzymology*
Metals / pharmacology
Sulfates / metabolism*
Sulfotransferases / metabolism*
Sulfur Radioisotopes
Tumor Cells, Cultured
Tyrosine / analogs & derivatives*,  metabolism*
Reg. No./Substance:
0/Metals; 0/Sulfates; 0/Sulfur Radioisotopes; 10028-17-8/Tritium; 55520-40-6/Tyrosine; 66-81-9/Cycloheximide; 956-46-7/tyrosine O-sulfate; EC 2.8.2.-/Sulfotransferases

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