= Corticosteroid-binding globulin
<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.<A role for corticosteroid-binding globulin in delivery of cortisol to activated neutrophils by G. L. Hammond and others>[Journal of Clinical Endocrinology and Metabolism 71, pp. 34–39; abstract, plasma transport and glycosylated cleavage products]{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.<A role for corticosteroid-binding globulin in delivery of cortisol to activated neutrophils by G. L. Hammond and others>[Abstract; elastase cleavage, cortisol release and absence of enzyme inhibition]{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.
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