A cadea alfa das hormonas glicoproteicas ou subunidade alfa das hormonas glicoproteicas é unha proteína que nos seres humanos está codificada polo xene CGA situado no cromosoma 6, a cal está presente en catro hormonas humanas.^[1]

As catro hormonas glicoproteicas humanas: gonadotropina coriónica humana (hCG), hormona luteinizante (LH), hormona estimulante dos folículos (FSH), e hormona estimulante da tiroide (TSH) son dímeros que constan dunha subunidade alfa común practicamente idéntica en todas elas ^[2], e unha subunidade beta diferente, que lles confire a súa especificidade biolóxica. As dúas cadeas están unidas non covalentemente. A proteína alfa codificada por este xene pertence á familia da cadea alfa das hormonas glicoproteicas.^[3]

A cadea alfa ten a seguinte secuencia de aminoácidos:

NH₂ - Ala - Pro - Asp - Val - Gln - Asp - Cys - Pro - Glu - Cys - Thr - Leu - Gln - Glu - Asn - Pro - Phe - Phe - Ser - Gln - Pro - Gly - Ala - Pro - Ile - Leu - Gln - Cys - Met - Gly - Cys - Cys - Phe - Ser - Arg - Ala - Tyr - Pro - Thr - Pro - Leu - Arg - Ser - Lys - Lys - Thr - Met - Leu - Val - Gln - Lys - Asn - Val - Thr - Ser - Glu - Ser - Thr - Cys - Cys - Val - Ala - Lys - Ser - Tyr - Asn - Arg - Val - Thr - Val - Met - Gly - Gly - Phe - Lys - Val - Glu - Asn - His - Thr - Ala - Cys - His - Cys - Ser - Thr - Cys - Tyr - Tyr - His - Lys - Ser - COOH

As cadeas alfa das catro hormonas denomínanse FSHA, LHA, TSHA e CGA.

• Gonadotropina

• Roger M, Lahlou N, Couzinet B; et al. (1990). "[Free alpha-subunit glycoprotein hormones: physiological and pathological data]". J. Steroid Biochem. 33 (4B): 763–9. PMID 2481154. doi:10.1016/0022-4731(89)90489-5. 
• Pierce JG (1972). "Eli Lilly lecture. The subunits of pituitary thyrotropin--their relationship to other glycoprotein hormones.". Endocrinology 89 (6): 1331–44. PMID 5002675. doi:10.1210/endo-89-6-1331. 
• Kourides IA, Gurr JA, Wolf O (1984). "The regulation and organization of thyroid stimulating hormone genes.". Recent Prog. Horm. Res. 40: 79–120. PMID 6207569. 
• Miyoshi I, Kasai N, Hayashizaki Y (1994). "[Structure and regulation of human thyroid-stimulating hormone (TSH) gene]". Nippon Rinsho 52 (4): 940–7. PMID 8196184. 
• Barrios-De-Tomasi J, Timossi C, Merchant H; et al. (2002). "Assessment of the in vitro and in vivo biological activities of the human follicle-stimulating isohormones.". Mol. Cell. Endocrinol. 186 (2): 189–98. PMID 11900895. doi:10.1016/S0303-7207(01)00657-8. 
• Moyle WR, Bahl OP, März L (1976). "Role of carbohydrate of human chorionic gonadotropin in the mechanism of hormone action.". J. Biol. Chem. 250 (23): 9163–9. PMID 172504. 
• Fiddes JC, Goodman HM (1979). "Isolation, cloning and sequence analysis of the cDNA for the alpha-subunit of human chorionic gonadotropin.". Nature 281 (5730): 351–6. PMID 481597. doi:10.1038/281351a0. 
• Sairam MR, Li CH (1977). "Human pituitary thyrotropin. The primary structure of the alpha and beta subunits.". Can. J. Biochem. 55 (7): 755–60. PMID 890569. doi:10.1139/o77-108. 
• Morgan FJ, Birken S, Canfield RE (1975). "The amino acid sequence of human chorionic gonadotropin. The alpha subunit and beta subunit.". J. Biol. Chem. 250 (13): 5247–58. PMID 1150658. 
• Rathnam P, Saxena BB (1975). "Primary amino acid sequence of follicle-stimulating hormone from human pituitary glands. I. alpha subunit.". J. Biol. Chem. 250 (17): 6735–46. PMID 1158880. 
• Weisshaar G, Hiyama J, Renwick AG, Nimtz M (1991). "NMR investigations of the N-linked oligosaccharides at individual glycosylation sites of human lutropin.". Eur. J. Biochem. 195 (1): 257–68. PMID 1991473. doi:10.1111/j.1432-1033.1991.tb15702.x. 
• Sakakibara R, Yokoo Y, Yoshikoshi K; et al. (1988). "Subcellular localization of intracellular forms of human chorionic gonadotropin in first trimester placenta.". J. Biochem. 102 (5): 993–1001. PMID 2449427. 
• Matzuk MM, Keene JL, Boime I (1989). "Site specificity of the chorionic gonadotropin N-linked oligosaccharides in signal transduction.". J. Biol. Chem. 264 (5): 2409–14. PMID 2536708. 
• Lustbader JW, Birken S, Pileggi NF; et al. (1990). "Crystallization and characterization of human chorionic gonadotropin in chemically deglycosylated and enzymatically desialylated states.". Biochemistry 28 (24): 9239–43. PMID 2611225. doi:10.1021/bi00450a001. 
• Harris DC, Machin KJ, Evin GM; et al. (1989). "Preliminary X-ray diffraction analysis of human chorionic gonadotropin.". J. Biol. Chem. 264 (12): 6705–6. PMID 2708337. 
• Hayashizaki Y, Miyai K, Kato K, Matsubara K (1985). "Molecular cloning of the human thyrotropin-beta subunit gene.". FEBS Lett. 188 (2): 394–400. PMID 3839756. doi:10.1016/0014-5793(85)80409-9. 
• Bellisario R, Carlsen RB, Bahl OP (1973). "Human chorionic gonadotropin. Linear amino acid sequence of the alpha subunit.". J. Biol. Chem. 248 (19): 6796–809. PMID 4745444. 
• Shome B, Parlow AF (1974). "Human follicle stimulating hormone (hFSH): first proposal for the amino acid sequence of the alpha-subunit (hFSHa) and first demonstration of its identity with the alpha-subunit of human luteinizing hormone (hLHa).". J. Clin. Endocrinol. Metab. 39 (1): 199–202. PMID 4835135. doi:10.1210/jcem-39-1-199.