The latter proteins are of unknown function.
Animals possess multiple isoforms of each type.
For example, four KCl cotransporter isoforms have been identified in humans. Each of the major types of CCC family members in mammals exist as paralogous isoforms. These may differ in substrates transported. The molecular physiology of electroneutral cation-chloride cotransport. Cloning and characterization of KCC3 and KCC4, new members of the cation-chloride cotransporter gene family.