Biology Reference
In-Depth Information
Although their conclusion that the lipid bilayer is the fundamental building block of
membranes is now universally recognized to be at the heart of membrane structure, it is
evident how lucky Gorter and Grendel were. The erythrocyte is perhaps the only eukaryotic
cell that would give a ratio of monolayer area to cell surface area of 2. All other eukaryotic
cells have extensive internal membranes that would significantly affect these measurements.
The prediction that there is exactly enough lipid to surround a cell twice means the lipid
bilayer had to constitute 100% of the membrane surface. There is no room for integral
membrane proteins! Benzene is a poor solvent for extracting polar lipids. Gorter probably
extracted only ~70% of the membrane lipids. These authors did not compress their mono-
layer to biological pressures and they also miscalculated the surface area of an erythrocyte
bi-concave disk! All of these errors conveniently canceled each other out resulting in
a nice, interpretable ratio of 2. The only data table reported in their seminal paper is shown
in Figure 2.12 . Gorter went on to publish more than 50 additional papers, but all on proteins.
Grendel ceased publishing in 1929.
1925 turned out to be a crucial year for the beginning of lipid bilayer studies. While Gorter
and Grendel used the general, undefined term 'lipoid' to describe the nature of the bilayer
component, J.B. Leathes and H.S. Raper in their 1925 topic The Fats [16] , suggested phospho-
lipids might be essential structural elements of cell membranes. Also in 1925, the American,
Hugo Fricke, used electrical impedance measurements to determine the thickness of the
erythrocyte membrane [17] . His value of 33 ˚ was essentially correct but he did not recognize
it as a bilayer. This is surprising since his value is approximately twice the lipid monolayer
values of ~13 to 16 ˚ reported by Pockels, Rayleigh, and Langmuir. In 1926 James B. Sumner
reported isolation of the first enzyme, urease, an astonishing feat in its day [18] . For this work,
Sumner was a co-recipient of the 1946 Nobel Prize in Chemistry. Sumner accomplished his
work despite having lost his left arm (he was left handed) in a hunting accident when he
was 17 years old. His wife, Cid Ricketts Sumner, wrote a topic that was adapted into the
popular 1957 movie Tammy and the Bachelor.
It is ironic that urea was the central compound in two of the major breakthroughs in
biochemistry, Wohler's first synthesis of an organic molecule (urea) from an inorganic mole-
cule (ammonium cyanate) in 1828 and Sumner's 1926 purification of urease. So, by the late
1920s, all pieces were in place to establish a realistic, working model for a biological
membrane. This membrane model first appeared in a 1935 article by Davson and Danielli
(Chapter 8).
SUMMARY
Membrane history has a very colorful past that followed two distinct paths. One path
investigated lipid monolayers (oil on water), while the other monitored the plasma
membrane of living cells. The first oil on water experiment is attributed to Ben Franklin in
1772. The Franklin experiment was greatly refined and quantified in the 1880s by Agnes
Pockels, a most remarkable woman. Despite being an uneducated homemaker, at the age
of 18 Pockels used old pots and pans, sewing threads and buttons to measure lipid mono-
layer properties. Pockel's methodologies were further refined in 1917 by Irwin Langmuir,
“The Dean of Surface Chemists”.
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