HUPUV PROTEINS OF RHODOBACTER-CAPSULATUS CAN BIND H-2 - EVIDENCE FROMTHE H-D EXCHANGE-REACTION

The H-D exchange reaction has been measured with the D-2-H2O system, f or Rhodobacter capsulatus JP91, which lacks the hupSL-encoded hydrogen ase, and R, capsulatus BSE16, which lacks the HupUV proteins, The hupU V gene products, expressed from plasmid pAC206, are shown to catalyze an H-D exchange reaction distinguishable from the H-D exchange due to the membrane-hound, hupSL-encoded hydrogenase, In the presence of O-2, the uptake hydrogenase of BSE16 cells catalyzed a rapid uptake and ox idation of H-2, D-2, and HD present in the system, and its activity (H -D exchange, H-2 evolution in presence of reduced methyl viologen [MV( +)]) depended on the external pH, while the H-D exchange due to HupUV remained insensitive to external pH and O-2. These data suggest that t he HupSL dimer is periplasmically oriented, while the HupUV proteins a re in the cytoplasmic compartment.