THE ENZYME IS A TRIMER OF *AB* SUBUNITS. TWO TRIMERS, RELATED BY A TWO-FOLD ROTATION, CAN FORM A HEXAMER. EACH *AB* SUBUNIT CONTAINS TWO CHAINS RESULTING FROM AN AUTOCATALYTIC CLEAVAGE REACTION. THE BETA CHAIN IS RESIDUES 1 THROUGH 81, WHILE THE ALPHA CHAIN IS RESIDUES 82 THROUGH 310. RESIDUE PVL 82 IS AN N-TERMINAL PYRUVOYL GROUP USED AS A COFACTOR. EACH COMPLETE *AB* SUBUNIT CONSISTS OF A BETA CHAIN AND A PVL COFACTOR LINKED TO THE N TERMINUS OF AN ALPHA CHAIN. / TWO "AB" SUBUNITS, RELATED BY A NON-CRYSTALLOGRAPHIC TWO-FOLD ROTATION IN A TAIL-TO-TAIL MANNER, CONSTITUTE THE ASYMMETRIC UNIT. THIS REPRESENTS ONE-THIRD OF THE BIOLOGICAL HEXAMER. / THE SECOND ONE-THIRD OF THE HEXAMER IS ASSEMBLED BY APPLYING THE CRYSTALLOGRAPHIC THREE-FOLD OPERATOR: -Y, X-Y, Z / THE THIRD ONE-THIRD OF THE HEXAMER IS ASSEMBLED BY APPLYING THE CRYSTALLOGRAPHIC THREE-FOLD OPERATOR: Y-X, -X, Z