Rhodopsin-like Protein from the Purple Membrane of <Emphasis Type="Italic">Halobacterium halobium</Emphasis>

HALOPHILIC bacteria require high concentrations of sodium chloride and lower concentrations of KCl and MgCl₂ for growth. The cell membrane dissociates into fragments of varying size when the salt is removed¹. One characteristic fragment—termed the “purple membrane” because of its characteristic deep purple colour—has been isolated in relatively pure form from Halobacterium halobium². We can now show that the purple colour is due to retinal bound to an opsin-like protein, the only protein present in this membrane fragment (see also ref. 3).