Transcortin

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]

Transcortin binds several steroid hormones at high rates:

• Cortisol - Approximately 90% of the cortisol in circulation is bound to transcortin. (The rest is bound to serum albumin.) Cortisol is thought to be biologically active only when it is not bound to transcortin.^{[citation needed]}
• Cortisone^[8]
• Deoxycorticosterone (DOC)^[8]
• Corticosterone - About 78% of serum corticosterone is bound to transcortin.
• Aldosterone - Approximately 17% of serum aldosterone is bound to transcortin, while another 47% is bound to serum albumin. The remaining 36% is free.^[9]
• Progesterone - Approximately 18% of serum progesterone is bound to transcortin, while another 80% of it is bound to serum albumin. The remaining 2% is free.^[10]
• 17α-Hydroxyprogesterone^[8]

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]}

Transcortin is produced by the liver and is increased by estrogens.^[12]

Mutations in this gene are rare. Only four mutations have been described, often in association with fatigue and chronic pain.^[13] The 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]

• Serpin
• Circaseptan, 7-day biological cycle