RHEA - Reaction directions

A reaction can occur in two directions:

  • left to right (LR, =>)
  • right to left (RL, <=)

But it can be the case that the reaction occurs in both directions at the same time:

  • bidirectional (BI, <=>), i.e. LR and RL

It can also be the case that the reaction occurs in an unknown or unspecified direction:

  • unspecified/unknown (UN, <?>), i.e. LR or RL or BI

This set of four reactions are tightly related, as they share the same participants. Any change in one of the reactions should be reflected in the other three, and their textual representations and fingerprints updated accordingly.
In fact, the participants are stored in the database only once, not four times (not only for space considerations, but for consistency and to avoid the hassle and errors due to having four copies of the same data).
So one of them - UN - is considered arbitrarily as the access point to the participants. That's why we need a UN_REACTION column in the INTENZ_REACTIONS table.