International Society of Photosynthesis Research
THE ABSTRACT BOOK , THE HOME PAGE , and MIRROR SITE
PROTON-TRANSLOCATING TRANSHYDROGENASE FROM PHOTOSYNTHETIC BACTERIA
Jackson J.B., Quirk P.G., Cotton N.P.J., Venning J.D., Gupta S., Peake S.J., Jeeves M., Smith K.J.
School of Biochemistry, University of Birmingham, UK
Transhydrogenase, which uses the energy of Dp to drive the reduction of NADP+ by NADH, has a tripartite structure. Domain I and domain III, which have the binding sites for NAD(H) and NADP(H), respectively, protrude from the membrane. Domain II spans the membrane. Stopped-flow spectroscopy on isolated, recombinant domains I and III shows that hydride transfer proceeds directly between the two nucleotides without intervention of any redox intermediates. A mobile loop region on the surface of domain I folds down and makes contact with the adenosine part of NADH when the nucleotide binds to the protein. Mutants in the loop inhibit the hydride transfer reaction (by 98% in Tyr235Asn). From NMR spectroscopy amino acid residues involved in the interaction between domains I and III are identified. These will be discussed with reference to our understanding of the three-dimensional structure of the proteins.