Hydrophobic membrane protein from chromatophores of Rhodospirillum rubrum. Structural and spectroscopic studies of monolayers and multilayers.
A hydrophobic, lipid- and pigment-free polypeptide from the chromatophore membrane of Rhodospirillum rubrum was spread from chloroform/methanol, pyridine and formic acid solutions at an air-water interface. Surface pressure versus area isotherms of the monolayers formed at the interface were partially dependent upon the spreading solvent used. From the surface area at 20 dynes/cm compression, an average molecular area of 12.9 nm2/molecule was calculated for a polypeptide monolayer spread from chloroform/methanol. Multilayers built up on germanium plates at different surface pressures were subjected to attenuated total reflection infrared spectroscopy. In all cases the amide I and II absorption bands were typical of alpha-helical and random conformations. Electron microscopy of transferred monolayers replicated by rotary platinum shadowing revealed domains of regular texture in specimens prepared at 20 dynes/cm. Such domains were virtually absent in specimens prepared at 10 and 30 dynes/cm. Light optical diffractometry of the ordered arrays yielded a smallest repetitive area of 13.5 nm2 which agrees well with the molecular area obtained from the monolayer surface. Although no drastic changes in secondary structure were detected in the course of this study, some conformational changes are indicated by solvent-dependent differences in the surface pressure versus area isotherms.
D020130:Bacterial Chromatophores / Q000648:ultrastructure; D001426:Bacterial Proteins; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D008027:Light; D008565:Membrane Proteins; D008854:Microscopy, Electron; D012247:Rhodospirillum rubrum / Q000648:ultrastructure; D012542:Scattering, Radiation; D012995:Solubility; D013055:Spectrophotometry, Infrared
D001426:Bacterial Proteins; D008565:Membrane Proteins