= Golgi lumen
{c}
The <Golgi lumen> is the enclosed interior of a <Golgi cisterna>, distinct from the surrounding <cytosol>.
The membrane-sidedness rule in <secretory protein routing> still applies within the <Golgi apparatus>. For a local worked example, stipulate a <membrane protein> with a <carbohydrate> chain exposed to <Golgi lumen> and a tail exposed to <cytosol>. An <enzyme> confined to <Golgi lumen> can contact that chain, but cannot directly contact the cytosolic tail without a boundary-crossing step. A change in which <Golgi cisterna> contains the <protein> need not turn the <protein> over. Thus chemical accessibility and cargo location are different questions: moving cargo onward preserves its membrane sides under the budding and fusion operations described in <secretory protein routing>.
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