Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
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.
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).
Binding
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.
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.
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.
In addition, approximately 4% of serum testosterone is bound to transcortin. A similarly small fraction of serum estradiol is bound to transcortin as well.
Synthesis
Transcortin is produced by the liver and is increased by estrogens.
Clinical significance
Mutations in this gene are rare. Only four mutations have been described, often in association with fatigue and chronic pain. 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.
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.
Musa BU, Seal US, Doe RP (September 1965). "Elevation of certain plasma proteins in man following estrogen administration: a dose-response relationship". J. Clin. Endocrinol. Metab. 25 (9): 1163–6. doi:10.1210/jcem-25-9-1163. PMID4284083.
Rosner W, Beers PC, Awan T, Khan MS (1976). "Identification of corticosteroid-binding globulin in human milk: measurement with a filter disk assay". J. Clin. Endocrinol. Metab. 42 (6): 1064–73. doi:10.1210/jcem-42-6-1064. PMID932172.
Smith CL, Power SG, Hammond GL (1992). "A Leu----His substitution at residue 93 in human corticosteroid binding globulin results in reduced affinity for cortisol". J. Steroid Biochem. Mol. Biol. 42 (7): 671–6. doi:10.1016/0960-0760(92)90107-T. PMID1504007. S2CID45601231.
Loric S, Egloff M, Domingo M, et al. (1990). "Immunochemical characterization of corticosteroid-binding globulin in human bronchoalveolar fluid". Clin. Chim. Acta. 186 (1): 19–23. doi:10.1016/0009-8981(89)90198-8. PMID2612005.
Heubner A, Belovsky O, Müller W, et al. (1987). "Application of liquid-liquid partition chromatography in the simultaneous purification of sex-hormone-binding globulin and corticosteroid-binding globulin". J. Chromatogr. 397: 419–34. doi:10.1016/S0021-9673(01)85027-5. PMID2821037.
Bardin CW, Gunsalus GL, Musto NA, et al. (1988). "Corticosteroid binding globulin, testosterone-estradiol binding globulin, and androgen binding protein belong to protein families distinct from steroid receptors". J. Steroid Biochem. 30 (1–6): 131–9. doi:10.1016/0022-4731(88)90085-4. PMID3386241.
Hammond GL, Langley MS (1986). "Identification and measurement of sex hormone binding globulin (SHBG) and corticosteroid binding globulin (CBG) in human saliva". Acta Endocrinol. 112 (4): 603–8. doi:10.1530/acta.0.1120603. PMID3751467.
Agrimonti F, Frairia R, Fornaro D, et al. (1983). "Circadian and circaseptan rhythmicities in corticosteroid-binding globulin (CBG) binding activity of human milk". Chronobiologia. 9 (3): 281–90. PMID7172869.
Maruyama K, Sugano S (1994). "Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides". Gene. 138 (1–2): 171–4. doi:10.1016/0378-1119(94)90802-8. PMID8125298.
Avvakumov GV, Hammond GL (1994). "Glycosylation of human corticosteroid-binding globulin. Differential processing and significance of carbohydrate chains at individual sites". Biochemistry. 33 (19): 5759–65. doi:10.1021/bi00185a012. PMID8180202.
Van Baelen H, Power SG, Hammond GL (1993). "Decreased cortisol-binding affinity of transcortin Leuven is associated with an amino acid substitution at residue-93". Steroids. 58 (6): 275–7. doi:10.1016/0039-128X(93)90072-U. PMID8212073. S2CID25160586.
Misao R, Nakanishi Y, Fujimoto J, et al. (1996). "Expression of corticosteroid-binding globulin mRNA in human uterine endometrial cancers". Steroids. 60 (10): 720–4. doi:10.1016/0039-128X(95)00106-Z. PMID8539782. S2CID37077783.
Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, et al. (1997). "Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library". Gene. 200 (1–2): 149–56. doi:10.1016/S0378-1119(97)00411-3. PMID9373149.