The invention provides isolated nucleic acids and their encoded polypeptides that are involved in enhancing the essential amino acid content of a plant. The polypeptide may be derived from a protease inhibitor, and more specifically, a chymotrypsin inhibitor. Chymotrypsin inhibitors that may be modified for use in the invention are present in many plant species. Barley (Hordeum vulgare) was initially used to obtain the chymotrypsin inhibitor modified for use in the present invention. Other plant species that may be used as a source for chymotrypsin inhibitor for use in the present invention include Zea Mays, Vicia faba, Cucurbita maxima, Canavalia lineata, Vigna angularis, Nicotiana tabacum, Nicotiana sylvestris, Sambucus nigra, Momordica charantia, Solanum tuberosum, Lycopersicon peruvianum, Lycopersicon esculentum, Amaranthus caudatus and Arabidopsis thalania. Optionally there is also a decrease in protease inhibitory activity of the polypeptide. The invention further provides recombinant expression cassettes, host cells, transgenic plants, and antibody compositions. The present invention provides methods and compositions relating to increasing essential amino acid content of plants for feed.

vigna racemosa/nicotine

Proteins with increased levels of essential amino acids

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