Gamma carbonic anhydrase-like: This family is composed of gamma carbonic anhydrase (CA), Ferripyochelin Binding Protein (FBP), E. coli paaY protein, and similar proteins. CAs are zinc-containing enzymes that catalyze the reversible hydration of carbon dioxide in a two-step mechanism, involving the nucleophilic attack of a zinc-bound hydroxide ion on carbon dioxide, followed by the regeneration of the active site by ionization of the zinc-bound water molecule and removal of a proton from the active site. They are ubiquitous enzymes involved in fundamental processes like photosynthesis, respiration, pH homeostasis and ion transport. There are three evolutionary distinct groups - alpha, beta and gamma carbonic anhydrases - which show no significant sequence identity or structural similarity. Gamma CAs are trimeric enzymes with left-handed parallel beta helix (LbH) structural domain.