Transcortin, also corticosteroid-binding globulin or CBG, is officially called serpin peptidase inhibitor, clade A (alpha-1 antiproteinase, antitrypsin), member 6.

It is an alpha-globulin.

Binding

Transcortin binds several steroid hormones:

• Cortisol
  Cortisol
  Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
  
  . Approximately 75% of the cortisol in circulation is bound to this plasma protein. (The rest is bound to serum albumin
  Serum albumin
  Serum albumin, often referred to simply as albumin is a protein that in humans is encoded by the ALB gene.Serum albumin is the most abundant plasma protein in mammals. Albumin is essential for maintaining the osmotic pressure needed for proper distribution of body fluids between intravascular...
  
  .) The cortisol is thought to be biologically active only when it is not bound to transcortin.

• Progesterone
  Progesterone
  Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...
  
  

• Aldosterone
  Aldosterone
  Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
  
  

• 11-Deoxycorticosterone
  11-Deoxycorticosterone
  11-Deoxycorticosterone is a steroid hormone produced by the adrenal gland that possesses mineralocorticoid activity and acts as a precursor to aldosterone. As its names indicate, it can be understood as 21-hydroxy- variant of progesterone or a 11-deoxy- variant of corticosterone...
  
   (DOC)

Production

Transcortin is produced by the liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

 and is regulated by estrogen

Estrogen

Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...

s. Therefore, plasma transcortin levels increase during pregnancy

Pregnancy

Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

, and are decreased in cirrhosis

Cirrhosis

Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules , leading to loss of liver function...

.

Clinical

Mutations in this gene are rare. To date only five cases have been reported. All cases have been associated with generalised pain and fatigue. 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.