A COMPARATIVE-STUDY ON THE PORINS OF RHODOBACTER-CAPSULATUS STRAINS 37B4 AND B10 GROWN UNDER DIFFERENT CULTURE CONDITIONS

The cell wall protein composition and the isolated porins of Rhodobact er capsulatus strains 37b4 and B10 were comparatively studied. The por ins from the two strains migrated differently on SDS-PAGE in the absen ce (oligomers: M(r) 92 000 and 89 000, monomers: M(r) 44 000 and 32 00 0, for strains 37b4 and B10, respectively) and in the presence of 8 M urea. N-terminal sequencing of the two purified porins demonstrated th at the sequences were different in five positions out of 21 positions determined. With both strains, the cell walls showed no growth conditi on dependent differences in their protein patterns. In both cases, onl y the porin given above was expressed in photoorganoheterotrophically (organotrophic) and photolithoautotrophically (lithotrophic) grown cel ls. There was also no difference between cells grown with glucose inst ead of malic acid or even using cells grown under phosphate starvation . In lipid bilayer experiments the isolated porins from Rhodobacter ca psulatus 37b4 and B10 had virtually the same single-channel properties . Furthermore, the porins obtained from cells grown under the given va rious different culture conditions revealed the same single-channel co nductance. In all cases a slight cation-selectivity was observed.