Plant oligoadenylates: enzymic synthesis, isolation, and biological activities
- 1 January 1985
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 24 (3) , 593-599
- https://doi.org/10.1021/bi00324a008
Abstract
An enzyme that converts [3H, 32P]ATP, with a 3H:32P ratio of 1:1, to oligoadenylates with the same 3H:32P ratio was increased in plants following treatment with human leukocyte interferon or plant antiviral factor or inoculation with tobacco mosaic virus. The enzyme was extracted from tobacco leaves, callus tissue cultures or cell suspension cultures. The enyzme, a putative plant oligoadenylate synthetase, was immobilized on poly(rI).cntdot.poly(rC)-agarose columns and converted ATP into plant oligoadenylates. These oligoadenylates were displaced from DEAE-cellulose columns with 350 mM KCl buffer, dialyzed and further purified by high-performance liquid chromatography (HPLC) and DEAE-cellulose gradient chromatography. In all steps of purification, the ratio of 3H:32P in the oligoadenylates remained 1:1. The plant oligoadenylates isolated by displacement with 350 mM KCl had a MW > 1000. The plant oligoadenylates had charges of 5.sbd. and 6.sbd.. HPLC resolved 5 peaks 3 of which inhibited protein synthesis in reticulocyte and wheat germ systems. Partial structural elucidation of the plant oligoadenylates was determined by enzymatic and chemical treatments. An adenylate with a 3'',5''-phosphodiester and/or a pyrophosphoryl linkage with either 3''- or 5''-terminal phosphates is postulated on the basis of treatment of oligoadenylates with T2 RNAse, snake venom phosphodiesterase and bacterial alkaline phosphatase and acid and alkaline hydrolyses. The plant oligoadenylates at 8 .times. 10-7 M inhibit protein synthesis by 75% in lysates from rabbit reticulocytes and 45% in wheat germ cell-free systems. Unlike the mammalian 2'',5''-oligodadenylate triphosphates, the plant oligoadenylates inhibited protein synthesis without activating the 2'',5''-A-dependent endonuclease from lysates of rabbit reticulocytes and without competing for 2'',5''-p3A4[32P]pCp binding to the endonuclease. In addition, the plant extracts do not contain any binding protein as determined by lack of binding of 2'',5''-p3A4[32P]pCp. These results suggest that the plant oligoadenylates differ substantially from the mammalian 2'',5''-oligoadenylates.Keywords
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