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Articles

Cell-free Synthesis of Globulin by Developing Oat (Avena sativa L.) Seeds ¹

^a Agricultural Research Service, United States Department of Agriculture and Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706

The primary storage protein synthesized during oat (Avena sativa L.) groat development is a globulin. Polysomes were isolated from oat groats 12 days after anthesis. These polysomes directed the incorporation of radioactive amino acids into protein in a cell-free protein synthesis system containing wheat germ supernatant. The Mg²⁺ optimum was 4 mM, the pH optimum was 6-8, and the amount of amino acid incorporation depended on polysome concentration. Incorporation of amino acids was linear for about 10 min and approached a maximum after 20 min. Using the initiation inhibitor, T-2 toxin, it was determined that about 36% of the amino acid incorporation was due to the initiation of new polypeptide chains. The in vitro product co-electrophoresed with authentic oat groat globulin on polyacrylamide-sodium dodecyl sulfate (SDS) gels. The cyanogen bromide peptides of the in vitro product partially corresponded with those from authentic globulin when electrophoresed on polyacrylamide-SDS gels. These data suggest that the in vitro product is primarily oat globulin. The polysome population was separated into membrane-bound and free polysomes. Membrane-bound polysomes synthesized about twice the amount of protein as did free polysomes. Products synthesized in vitro on both types of polysomes were essentially the same.

³ To whom reprint requests should be addressed.

¹ Research supported by the Agricultural Research Service, United States Department of Agriculture, and by the College of Agricultural and Life Sciences and the Graduate School, University of Wisconsin, Madison.