Definition: An interaction in which molecules of one or more physicalEntity pools are physically transformed and become a member of one or more other physicalEntity pools. Comments: Conversions in BioPAX are stoichiometric and closed world, i.e. it is assumed that all of the participants are listed. Both properties are due to the law of mass conservation. Usage: Subclasses of conversion represent different types of transformation reflected by the properties of different physicalEntity. BiochemicalReactions will change the ModificationFeatures on a PhysicalEntity , Transport will change the CellularLocation and ComplexAssembly will change BindingFeatures. Generic Conversion class should only be used when the modification does not fit into one of these classes. Example: Opening of a voltage gated channel.
Source:http://www.biopax.org/release/biopax-level3.owl#Conversion