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General
Information:
Protect material from long-term exposure to light;
may be exposed to light for short periods of time.
Fluorescent Properties
Excitation:
460nm
Emission:
534nm
e
= 14,000 cm-1M-1 determined in chloroform
at 460nm.
Cholesterol is most often found distributed non randomly in the plane
of the bilayer,
giving rise to cholesterol-rich and -poor domains. Many of these domains
are thought
to be crucial for the maintenance of membrane structure and function.
However,
such well-characterized domains generally occur in the membranes that
contain
relatively large amounts of cholesterol. Cholesterol organization
in membranes
containing very low amounts of cholesterol has not been investigated
extensively.1
Avanti's new fluorescent cholesterol analogue provides the researcher
with the right
probe to explore this issue.
Beware
of short chain imitations!
Avanti offers a fluorescently tagged cholesterol which closely resembles
the structure of native
cholesterol. Avanti?s analogue, 25-NBD Cholesterol, incorporates into
membranes and more effectively
probes cholesterol containing domains, an obvious advantage over short-chain
analogues.
Cholesterol
Avanti's Fluorescent Cholesterol Analogue
Cholesterol is most often found distributed non randomly in the
plane of the bilayer, giving rise to
cholesterol-rich and cholesterol-poor domains. Many of these domains
are thought to be crucial for the maintenance of membrane structure
and function. However, such well-characterized domains generally
occur in the membranes that contain relatively large amounts of
cholesterol. Cholesterol organization in membranes containing very
low amounts of cholesterol has not been investigated extensively.
Recent evidence from differential-scanning calorimetric studies
suggest that cholesterol may not form uniform monodisperse solutions,
as assumed earlier, in the membranes even at very low concentrations.
Fluorescent cholesterol analogues, when chosen carefully, offer
a powerful approach for studying the distribution and organization
of cholesterol in membranes at low concentrations. In this paper,
we have studied the organization of cholesterol in membranes at
very low concentrations (up to 5 mol % of the total lipid) using
a fluorescent cholesterol analogue
(NBD-cholesterol) which is labeled with the 7- nitrobenz-2-oxa-1,3-diazol-4-yl
(NBD) group at the flexible acyl chain, without any alteration in
the structural features necessary for proper membrane incorporation.
Our results show that NBD-cholesterol exhibits local organization
even at very low concentrations. This is consistent with the recently
suggested model of cholesterol organization in membranes at low
concentrations, involving the formation of transbilayer, tail-to-tail
dimers [Harris, J.S., Epps, D. E., Davio, S. R., & Kezdy, F.J.
(1995) Biochemistry 34, 3851-3857]. The implications of such local
cholesterol organization in membranes that have very low cholesterol
content in vivo, such as the endoplasmic reticulum and the inner
mitochondrial membrane, open up interesting possibilities.
Mukherjee, S. and A. Chattopadhyay. (1996). Membrane organization
at low cholesterol concentrations: a study using 7-nitrobenz-2-oxa-1,3-diazol-4-yl-labeled
cholesterol. Biochemistry 35:1311-22.
