9.A.20 The Low Affinity Cation Transporter (LACatT) Family
A single member of the LACatT family has been sequenced and functionally characterized. This protein, LCT1 of Triticum aestivum (wheat), possesses about 570 amino acyl residues, 10 or 11 putative transmembrane α-helical spanners (TMSs) and a 200 residue hydrophilic amino terminus containing sequences enriched in proline, glutamate, serine and threonine (PEST). The transporter was shown to mediate low affinity (~10 mM) uptake of K , Rb , Na , Ca2 and Cd2 , but not Zn2 , in a yeast mutant strain deficient in K uptake. Several divalent metal ions (Mn2 , Zn2 , Pb2 , Cu2 ) inhibit transport. LCT1 is expressed in low abundance in wheat roots and leaves. The mode of transport and energy coupling mechanism (if any) are not known. A homologue is present in rice.
The generalized transport reaction believed to be catalyzed by LCT1 is:
cation (out) cation (in)