At each end of the glutenin chain are sulfur-containing amino acids that can form strong sulfur-sulfur bonds with the same amino acids at the ends of other glutenin chains. To do this they require the availability of oxidizing agents—oxygen in the air, certain substances produced by yeasts, or “dough improvers” (p. 529) added by the flour manufacturer or baker. The long, coiled middle stretch of the glutenin molecule consists mainly of amino acids that form weaker, temporary bonds (hydrogen and hydrophobic bonds) with similar amino acids. Glutenin chains thus link up with each other end-to-end to form super-chains a few hundred glutenins long, and coiled stretches along their lengths