Ribulose-phosphate binding barrel <p>The ribulose-phosphate binding barrel consists of a parallel beta-sheet barrel fold containing a phosphate-binding site. Several proteins display this fold, including histidine biosynthesis enzymes, tryptophan biosynthesis enzymes, D-ribulose-5-phosphate 3-epimerase, and decarboxylases [<cite idref="PUB00014262"/>].</p>