sentences:  In yeast and bacteria, orotate phosphoribosyltransferase is an independent enzyme with a unique gene coding for the protein, whereas in mammals and other multicellular organisms, the catalytic function is carried out by a domain of the bifunctional enzyme UMP synthase (UMPS).As OPRTase is part of a bifunctional complex UMP synthase in humans, the function and stability of this enzyme is not necessarily directly associated with disorders in the human body.It is however reasonable to believe that a dysfunction in one of the enzymes will cause a dysfunction of the whole enzyme.