 Although the overall fold of the human enzyme is similar to that of yeast, the human structure is different in that it has two loops that extend from the general protein structure and into the FAD binding sites when bound the NAD+ molecule, required for catalysis, is not close to the FAD moiety.However, when NADH is bound instead, it is stacked directly op top of the FAD central structure.The current hE3 structures show directly that the disease-causing mutations occur at three locations in the human enzyme