The amino acid/polyamine/organocation (APC) superfamily of transporters specific for amino acids, polyamines and organocations

In this paper an analysis of 175 currently sequenced transport proteins tha t comprise the amino acid/polyamine/organocation (APC) superfamily is repor ted. Members of this superfamily fall into 10 well-defined families that ar e either prokaryote specific, eukaryote specific or ubiquitous. Most of the se proteins exhibit 12 probable transmembrane spanners (TMSs), but members of two of these families deviate from this pattern, exhibiting 10 and 14 TM Ss. All members of these families are tabulated, their functional propertie s are reviewed and phylogenetic/sequence analyses define the evolutionary r elationships of the proteins to each other. Evidence is presented that the APC superfamily may include two other currently recognized families that ex hibit greater degrees of sequence divergence from APC superfamily members t han do the proteins of the 10 established families from each other. At leas t some of the protein members of these two distantly related families exhib it 11 established TMSs. Altogether, the APC superfamily probably includes 1 2 currently recognized families with members that exhibit exclusive specifi city for amino acids and their derivatives but which can possess 10, 11, 12 or 14 TMSs per polypeptide chain.