CHARACTERIZATION OF PORIN FROM ROSEOBACTER-DENITRIFICANS

Porin from Roseobacter denitrificans was isolated and purified to homo geneity. The pore characteristics from this marine bacterium were comp ared to those of its phylogenetically closely related freshwater bacte ria Rhodobacter capsulatus, Rhodobacter sphaeroides and Rhodopseudomon as blastica. The porin formed weakly cation-selective, general diffusi on pores in lipid bilayer membranes. High transmembrane potentials cau sed channel closing in steps that were of one or two thirds of the ini tial on-steps indicating that the porin of R. denitrificans comprised three more or less independent channels similar to PhoE and OmpC of Es cherichia coil and the porin of Rhodobacter capsulatus. 37b4 Predictio n of the secondary structure of the 36 N-terminal amino acid residues indicated two transmembrane beta-strands similar to those of the porin s of Rhodobacter capsulatus 37b4 and Rhodopseudomonas blastica. Differ ences of the single channel conductivities between the porin of R. den itrificans and those of the related freshwater bacteria show that R. d enitrificans evolved porin channels that are well adapted to the marin e habitat.