C-14-TYROSINE AND H-3-TYROSINE INCORPORATION INTO ASCIDIA CERATODES TUNICHROME IN-VIVO

Radiolabeled tyrosine is incorporated into newly biosynthesized tunich rome of Ascidia ceratodes at a rate comparable to previous findings wi th phenylalanine. H-3-tyrosine incorporation indicates that formation of the catechol and pyrogallol moieties occurs via the NIH shift pathw ay. Radiolabel is found in many compartments other than solely tunichr ome (tunic > whole body much greater than blood plasma >>> tunichrome) . The amount of label in the tunic, whole bodies and blood plasma decl ines over the 14 days following exposure to 3H-tyrosine, whereas the r adiolabel in the tunichrome continues to increase. These results are c onsistent with two alternative hypotheses: tunichromes may be formed e ither by sequential hydroxylation of di- and tri-peptide precursors, o r by selective cleavage of a larger DOPA- or TOPA-containing compound. In either event, hydroxylation may precede formation of tunichrome's carbon backbone. Copyright (C) 1996 Elsevier Science Inc.