Role of RhAG and AQP1 in NH3 and CO2 gas transport in red cell ghosts: a stopped-flow analysis

Specificity and Regulation of Interaction between the P II and AmtB 1 Proteins in Rhodospirillum rubrum

“…ADP inhibits the destabilization of the GlnJ-AmtB 1 complex in the presence of ATP and 2-KG, supporting a role for P II as an energy sensor measuring the ratio of ATP to ADP. In the presence of saturating levels of ATP, the estimated K d of 2-KG for GlnJ bound to AmtB 1 is 340 M, which is higher than that required for uridylylation of GlnJ in vitro, about 5 M. This supports a model where multiple 2-KG and ATP molecules must bind a P II trimer to stimulate release of P II from AmtB 1 , in contrast to the lower 2-KG requirement for productive uridylylation of P II by GlnD.The ammonium channel/rhesus (Amt/Rh) family of proteins is a widely distributed group of trimeric integral membrane proteins found in all domains of life that can function as gas channels of ammonia and perhaps carbon dioxide (13,20,29,39,43). A subset of this family, the AmtB proteins, is found in bacteria, archaea, some lower eukaryotes and plants.…”

“…The ammonium channel/rhesus (Amt/Rh) family of proteins is a widely distributed group of trimeric integral membrane proteins found in all domains of life that can function as gas channels of ammonia and perhaps carbon dioxide (13,20,29,39,43). A subset of this family, the AmtB proteins, is found in bacteria, archaea, some lower eukaryotes and plants.…”

The monovalent cation leak in overhydrated stomatocytic red blood cells results from amino acid substitutions in the Rh-associated glycoprotein

“…Its homology to the Amt proteins suggests that it may act as a cation channel transporting NH 4 ϩ , or as a gas channel moving NH 3 or CO 2 . However, early studies of the transport properties of human RhAG gave conflicting results, variously describing RhAG as a NH 3 /NH 4 ϩ exchanger or ammonium transporter, [28][29][30][31] or as an ammonia channel, [32][33][34] or suggesting that RhAG transports CO 2 , 35 or both CO 2 and NH 3 . 36 Recently, even the gas channel hypothesis has been disputed.…”

Ammonia and urea transporters in gills of fish and aquatic crustaceans

“…There is evidence that Rh1 transports CO 2 in a green alga (Kustu and Inwood, 2006), and Peng and Huang (Peng and Huang, 2006) have postulated that the divergence and rapid diversification of Rh proteins from the ancestral Amt proteins occurred as Rhs acquired the (additional) role of CO 2 transport, notably as red blood cell gas transfer function elaborated within the vertebrates. Indeed, RhAG transport of CO 2 has been demonstrated for red cell Rh proteins (Boron, 2006;Endeward et al, 2006), although this observation may be very technique dependent (Ripoche et al, 2006). Controversially, mRNA of a lepidopteran Rh protein was shown to be expressed at particularly low levels in the trachea of the caterpillar, a tissue specifically designed for O 2 /CO 2 exchange (Weihrauch, 2006).…”