Sulfation of L-tyrosine in higher plants and mammalian animals
1994
Suiko, M. | Sakakibara, Y. | Nakamura, T. | Ohashi, T. | Miura, M. (Miyazaki Univ., Miyazaki (Japan). Faculty of Agriculture) | Nakajima, H. (Unitika Research and Development Center, Kyoto (Japan). Biochemistry Dept.) | Zhang, X. | Liu, M. (The University of Texas Health Center at Tyler, Tyler (USA). Department of Biochemistry)
Corn (Zea mays L.) and pea (Pisum sativum L.) seedlings were labeled with (35S) sulfate to ascertain for the first time the occurrence of tyrosine-O-sulfation (or tyrosine sulfation) in higher plants. Both protein-bound tyrosine-o-(35S) sulfate were detected in the leaves and roots of two kinds of plant seedlings. Tyrosine sulfation was found to occur also in the proteins secreted from the roots into the growth media. No free tyrosine sulfate was detectable in the growth media. Different subcellular fractions (10,000 g pellets (Sorvall fraction), 140,000 g pellets, and 140,000 g supernatant) of corn seedling leaves were solubilized either with or without 1 Triton X-100 and assayed for the enzyme activity of tyrosine sulfation in vitro by labeling with (35 S)PAPS or (14 C)L-tyrosine for 1 hr at 25 Deg C in the presence of inhibitors of phosphatases and proteases. Only the Sorvall fraction (either with or without Triton) with (14C) L-tyrosine producted free (14C) tyrosine sulfate, whereas protein-bound (14C) tyrosine sulfate did not. It is inferred from the data that (1) free tyrosine sulfate could be formed from free tyrosine rather than from tyrosine sulfated proteins in the higher plants; (2) the enzyme(s) for tyrosine sulfation was (were) located in mitochondria or chloroplasts or both; however, the intact organelles were not required for the enzyme action. The assay also showed that the optimal pH for the enzyme action was 7.6.
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