EC 1 Oxidoreductases
EC 2 Transferases
EC 3 Hydrolases
EC 4 Lyases
EC 5 Isomerases
EC 6 Ligases

Organism-specific lists

E. coli [reactions assigned genes] [orphan activities]
S. cerevisiae [reactions assigned genes] [orphan activities]
B. subtilis [reactions assigned genes] [orphan activities]

How do we know if an activity is orphan or assigned to genes?