= Guanylate cyclase
<Guanylate cyclase> is an <enzyme> that converts <GTP> into <cyclic guanosine monophosphate>, releasing <diphosphate>. The official classification is EC 4.6.1.2. The phosphate retained in the product forms a cyclic linkage involving the <ribose> 3' and 5' positions.<Guanylate cyclase in IUBMB Enzyme Nomenclature>[Reaction and systematic name]{ref}
The reaction changes nucleotide connectivity rather than making the guanine-containing part from scratch. In an ideal closed assay with no competing reactions, forming $10\,\mathrm{nmol}$ of <cyclic guanosine monophosphate> consumes $10\,\mathrm{nmol}$ of <GTP> and produces $10\,\mathrm{nmol}$ of <diphosphate>. The enzyme's name specifies a chemical transformation; it does not identify a unique concentration or cellular rate.
Synthesis and accumulation also differ. If a <phosphodiesterase> simultaneously removes the cyclic product, its pool obeys a material balance,
$$
\frac{dC}{dt}=v_{\mathrm{synthesis}}-v_{\mathrm{removal}},
$$
with rates expressed in compatible concentration-per-time units. For constructed rates of $2\,\mathrm{nM\,s^{-1}}$ for both processes, the product concentration is constant even though both reactions are active.
Consequently, an assay of <guanylate cyclase> should distinguish product formation from net product accumulation, using defined conditions or an independent estimate of removal. A constant cyclic-nucleotide signal alone does not establish that synthesis has stopped.
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