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Adenylyl cyclase is a lyase
class enzyme that catalyzes the formation of cyclic adenosine monophosphate
from adenosine triphosphate. Adenylyl cyclase exists in three classes (I,
II, and III) and has nine isoforms in class III mammalian adenylyl cyclase.
It exists mainly in a membrane associated form but can also be found in
a soluble form depending on the organism or tissue. Adenylyl cyclase is
a major player in maintaining signal transduction pathways by converting
numerous extracellular hormonal signals into the form of a second messenger
in cyclic adenosine monophosphate. The active site, as well as some regulatory
sites, is formed as a result of dimerization of the enzymes two catalytic
domains, which is essential for catalysis. Regulation of adenylyl cyclase
is performed by activated G-proteins, calmodulin, P-site analog inhibitors,
phosphorylation, and forskolin, a hypotensive diterpene drug, at differing
regulatory sites. Two Mg2+ or Mn2+ ions are required to bind with adenosine
triphosphate in order for catalysis to occur. The production and regulation
of cyclic adenosine monophosphate is critically important in the activation
of several cellular metabolic processes, including enzyme activity, gene-expression
patterns, and membrane excitability, making correct adenylyl cyclase function
essential in the maintenance of normal physiology.
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