Protein found in humans
Transcortin, also known as corticosteroid-binding globulin (CBG) or serpin A6, is a protein produced in the liver in animals. In humans it is encoded by the SERPINA6 gene. It is an alpha-globulin.[5][6][7]
Function
This gene encodes an alpha-globulin protein with corticosteroid-binding properties. This is the major transport protein for glucocorticoids and progestins in the blood of most vertebrates. The gene localizes to a chromosomal region containing several closely related serine protease inhibitors (serpins).[7]
Binding
Transcortin binds several steroid hormones at high rates:
In addition, approximately 4% of serum testosterone is bound to transcortin.[11] A similarly small fraction of serum estradiol is bound to transcortin as well.[citation needed]
Synthesis
Transcortin is produced by the liver and is increased by estrogens.[12]
Clinical significance
Mutations in this gene are rare. Only four mutations have been described, often in association with fatigue and chronic pain.[13] This mechanism for these symptoms is not known. This condition must be distinguished from secondary hypocortisolism. Exogenous hydrocortisone does not appear to improve the fatigue.[citation needed]
Hepatic synthesis of corticosteroid-binding globulin more than doubles in pregnancy; that is, bound plasma cortisol in term pregnancy is approximately 2 to 3 times that of nonpregnant women.[14][15]