Tyramine-O-sulfate, in addition to tyrosine-O-sulfate, is produced and secreted by HepG2 human hepatoma cells, but not by 3Y1 rat embryo fibroblasts

Abstract

The spent media of HepG2 human hepatoma cells and 3Y1 rat embryo fibroblasts labeled with [35S]sulfate, upon ultrafiltration, were analyzed by a two-dimensional thin-layer separation procedure. Autoradiographs of the cellulose thin-layer plate revealed the presence of tyramine-O-[35S]sulfate in addition to tyrosine-O-[35S]sulfate in spent medium from human hepatoma cells. In contrast, only tyrosine-O-[35S]sulfate was observed in spent medium of 3Y1 rat fibroblasts. Using adenosine, 3'-phosphate, 5'-phospho[35S]sulfate as the sulfate donor, sulfotransferase(s) present in HepG2 cell homogenate catalyzed the sulfation of tyramine to tyramine-O-[35S]sulfate, but not the sulfation of tyrosine to tyrosine-O-[35S]sulfate. Endogenous aromatic amino acid decarboxylase present in HepG2 homogenate was shown to catalyze the decarboxylation of [3H]tyrosine to form [3H]tyramine while attempts to use it for the decarboxylation of tyrosine-O-sulfate to form tyramine-O-sulfate were unsuccessful. These results suggest that tyramine-O-sulfate may be derived from the de novo sulfation of tyramine, instead of the decarboxylation of tyrosine-O-sulfate.