1.2.9 Most membranes are electrically polarized with inside negative(--70 mV)(the membrane potential plays a key role in transport, energy conversion, and excitability). 1.3 Proteins attach to membranes in different wavs 1.3.1 Some proteins, called integral proteins span the lipid bilayer (e.g glycophorin in erythrocyte, bacteriorhodopsin in halobacterium halobacterium).1.2.9 Most membranes are electrically polarized with inside negative (~-70 mV) (the membrane potential plays a key role in transport, energy conversion, and excitability). 1.3 Proteins attach to membranes in different ways. 1.3.1 Some proteins, called integral proteins, span the lipid bilayer (e.g., glycophorin in erythrocyte, bacteriorhodopsin in halobacterium halobacterium)