Existence of a plant tyrosylprotein sulfotransferase: novel plant enzyme catalyzing tyrosine O-sulfation of preprophytosulfokine variants in vitro

An in vitro assay system to detect tyrosylprotein sulfotransferase (TPST) a ctivity of higher plant cells was established, using synthetic oligopeptide s based on the deduced amino acid sequence of a phytosulfokine-alpha (PSB-a lpha) precursor, TPST activity nas found in microsomal membrane fractions o f rice, asparagus and carrot cells and it was confirmed that acidic amino a cid residues adjacent to the tyrosine residues of acceptor peptides were es sential to the sulfation reaction. The asparagus TEST exhibited a broad pH optimum of 7.0-8.5, required manganese ions for maximal activity and appear ed to be a membrane-bound protein localized in the Golgi apparatus. These e nzymes should be defined as a new class of plant sulfotransferases that cat alyze tyrosine O-sulfation of a PSK-alpha precursor and other unknown prote ins. (C) 2000 Federation of European Biochemical Societies.