Formiminotransferase cyclodeaminase from porcine liver. An octomeric enzyme containing bifunctional polypeptides.

The forminiminotransferase-cyclodeaminase complex contains 2.8% carbohydrate and is composed of identical subunits based on molecular weight, isoelectric focusing and the number of CNBr-generated peptides. Electron microscopy demonstrated that the complex is a ring-shaped molecule when negatively stained both in solution and in crystalline structures. Rotational reinforcement of electron micrographs reveals that the molecule is composed of eight subunits arranged in a planar ring. These results indicate that each polypeptide of the complex must contain both enzymic activities.