|Budget Amount *help
¥1,800,000 (Direct Cost : ¥1,800,000)
Fiscal Year 1990 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1989 : ¥900,000 (Direct Cost : ¥900,000)
Energy transduction systems in living cells play important roles to maintain the homeostasis of the intra- and extra-cellular circumstances. Mitchell's chemiosmotic theory explained the energy transduction processes quite well. Among the energy transducing systems, the secondary active transport processes are understood by the chemiosmotic theory that the substrate is accumulated with the concomitant movement of the coupling ion(s) which is driven by the electrochemical gradient. However, the molecular mechanism of the chemiosmotic coupling has not been elucidated in detail.
In this study, first of all I have demonstrated that the molecular mechanism of the proline, lactose, and glutamate active transports of E coli is explained by the affinity model, where the co-substrates (coupling ion) which bind to carrier proteins enhance the conformational change of the proteins to acquire the affinity of the substrates. Secondly, the binding site of sodium, which is the coupling ion for the glut
amate and proline carriers of E. coli has been proposed as the five amino acid alignment in the amino acid sequences of these carrier proteins from the homology search of the amino acid sequences of these sodium co-transport carriers. Thirdly, from the biochemical and molecular biological studies of the proline carrier of E. coli, the amino acids in the substrate and co-substrate binding sites have been identified as play playing important roles in the active transport process. In addition, the orientation of the carrier protein in membrane has been elucidated.
The study of structure and function of the secondary active transport proteins is quite important in understanding the mechanism of the highly selective and highly efficient energy transducing machineries of biological systems. Especially, the question whether the active transport protein which operates according to the random binding mechanism instead of the affinity mechanism is possible as the biological energy transducing machinery should be answered in near future. Less