Neuraminidase enzyme. Molecular model of the viral enzyme neuraminidase. This enzyme is found on the surface of influenza (flu) viruses, and is essent- ial for the spread of viruses through the body. Atoms are represented as balls surrounded by dotted spheres, and are colour-coded: carbon (green), nitrogen (yellow) and oxygen (blue). Neuraminidase's purpose is to allow new viruses to exit the cell in which they were created. New drugs which have been designed to block neuramin- idase have been found to dramatically reduce the duration of the symptoms of influenza. Drug design using models such as this reduces the expenditure and time usually needed to create new drugs.