PANTHER: a pathway is modelled as PE and participates in a reaction

[IgorRodchenkov]

See, e.g., http://apps.pathwaycommons.org/view?uri=http%3A%2F%2Fidentifiers.org%2Fpanther.pathway%2FP04397
(SBGN view)

Obviously, the "Insulin signaling pathway" there is a PhysicalEntity that is 'left' participant of the reaction (this view results from a not recommended trick/hack in the original BioPAX model...)