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CASE FILES: BIOCHEMISTRY
[32.2] Prostaglandins comprise a family of oxygenated lipid signaling mole-
cules derived from polyunsaturated fatty acids such as arachidonic
acid. They are involved in regulating a number of cellular processes.
Some of the prostaglandins act to increase vasodilation and levels of
cAMP in cells, whereas others increase vaso- and bronchoconstriction
and smooth muscle contraction. In the conversion of arachidonic acid
to prostaglandins, the oxygenation step is accomplished by the enzyme
that synthesizes which of the following compounds?
A. Prostaglandin D2
B. Prostaglandin E2
C. Prostaglandin F2a
D. Prostaglandin H2
E. Prostaglandin I2
[32.3] Signaling via prostanoids begins by interaction of the prostanoid with
its receptor. The receptor involved is usually located in which part of
the cell?
A. Plasma membrane of a cell near the cell making the prostanoid
B. Nucleus of a cell in a different organ from the cell making the
prostanoid
C. Endoplasmic reticulum of the cell making the prostanoid
D. Lysosomes of a cell circulating in the blood
E. Golgi of a cell circulating in the blood
A nsw ers
[32.1]
C. The coxibs were designed to inhibit the activity of the inducible
form of PGH synthase so as not to inhibit the constitutive produc-
tion of prostaglandins and thromboxanes. They inhibit the first step
in the process, that catalyzed by the cyclooxygenase activity of PGH
synthase-2.
[32.2]
D. The first step in the synthesis of prostaglandins and thromboxanes
is the reaction catalyzed by the cyclooxygenase activity of PGH syn-
thase. This reaction causes the cyclization of the fatty acid while at the
same time introducing an unstable endoperoxide between carbons
9 and 10 and a hydroperoxide at carbon 15 to produce PGG2, which is
rapidly reduced to PGH2 by the peroxidase activity of PGH synthase.
[32.3]
A. The prostanoids have a wide variety of physiologic effects, but
they regulate these processes locally by binding to a receptor on the
plasma membrane of a cell close to where the prostanoid was syn-
thesized. Binding of the prostanoid to the receptor usually activates a
GTP-binding protein, which acts to activate (or inhibit) adenylate
cyclase or the phosphatidylinositol cascade.
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