Examples of a reaction rule with related reactions and a complicated reaction. (a) Main substrate and product of reactions catalyzed by ADH (EC126.96.36.199) are listed. The reaction rule explains every reaction in both of forward and backward directions. (b) An example of complicated reaction (leukotriene-A4-forming reaction) which is catalyzed by ec188.8.131.52. The reaction mechanism is hard to be defined as a rule.