Abstract:
ABSTRACT The lipid hinding properties of the membrane
protein cytochrome b:. (detergent-extracted from
calf liver microsomal preparations) were characterized by
studying the interaction of spin-labeled lipid,- (5-, 12-,
and 16-doxylstcaric acid and 5- and 16-cloxylphosphatidylcholine,
where cloxyl refers to the nitroxide moiety)
with cytochrome b :, using electron "pin resonance
spectroscopy. The intact cytochrome b, n1olec11lc immobilizes
all of the lipid spin label,;, while the segment of
cytochrome b, released by trypsin doei. not afTcct lipid
mobility. The immobilization of lipid spin label,-; on the
h) ·drophohic surface of intact cytochrome b:, is not appreciably
altered by associating the protein with liposomc"
· DHTcrcnccs in polarity of the lipid binding site"
between c, ·tochromc b, and phospholipid vc,.icles were also
ob,-cr\'ed. The lipid binding sites on cytochrome b.; arc
hydrophobic by conventional criteria, but arc more polar
than the interior of fluid phospholipid bilayers.