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Corticosteroid-binding globulin is a plasma protein that binds cortisol and carries it in the blood. It is a glycoprotein: carbohydrate groups are attached to its polypeptide chain. Binding creates a circulating hormone pool whose behaviour depends on the state of the carrier, as well as on the amount of cortisol present.^[ref]

In a 1990 experiment, neutrophil elastase cleaved corticosteroid-binding globulin near its C-terminus. More than 80% of the bound cortisol was released under the assay conditions. The carrier did not inhibit the enzyme; it served as a substrate. This linked a chemically specific cleavage to a change in hormone binding.^[ref]

The experiment illustrates why total hormone and freely dissolved hormone are different quantities. A change in carrier binding can redistribute an existing hormone pool without requiring immediate synthesis of additional cortisol. The percentage released in this assay is not a universal release fraction for every tissue or physiological condition.

G. L. Hammond investigated how circulating binding proteins influence access to steroid hormones. A 1990 study examined corticosteroid-binding globulin, a blood plasma protein that binds cortisol, and its interaction with neutrophil elastase.^[ref]

In the assay, neutrophil elastase cleaved corticosteroid-binding globulin near its terminal region and released more than 80% of its bound cortisol. The cleavage did not inhibit the enzyme. The work supplied a molecular mechanism by which a hormone-binding carrier can change local hormone availability, while the proposed physiological delivery role requires distinguishing an experimental mechanism from its magnitude in living tissue.^[ref]