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Cystine Content of Legume Seed Proteins: Estimation by Determination of Cysteine with 2-Vinylquinoline, and Relation to Protein Content and Activity of Cysteine Synthase

Department of Biochemistry, University of California, Riverside, California 92521

The cystine content of the protein of a number of different lines of legume seeds has been determined by the method of Krull et al. which selectively reacts cysteine residues of intact, reduced proteins with 2-vinylquinoline, giving an adduct with an absorption maximum at 318 nm. Some seed lines were found to have 3.5 times as much cysteine as the seed line with the lowest cysteine content, perhaps offering opportunities for improvement in the nutritional quality of bean seed proteins through breeding and selection. While no correlation between cysteine levels and protein content was observed, a positive correlation was found between the specific activity of the terminal enzyme of cysteine synthesis, cysteine synthase, and the cysteine content of seeds.

KEY WORDS: • cystine • 2-vinylquinoline • legume seed protein • cysteine synthase

¹ To whom requests for reprints should be addressed.

Manuscript received 10 November 1976.