Shared alpha chain of the active heterodimeric glycoprotein hormones thyrotropin/thyroid stimulating hormone/TSH, lutropin/luteinizing hormone/LH, follitropin/follicle stimulating hormone/FSH and choriogonadotropin/CG. These hormones bind specific receptors on target cells that in turn activate downstream signaling pathways. Heterodimer. The active hormones thyrotropin, lutropin, follitropin and choriogonadotropin are heterodimers composed of CGA, a common alpha chain described here and a unique beta chain which confers their biological specificity to the hormones: TSHB for thyrotropin, LHB for lutropin, FSHB for follitropin and choriogonadotropin subunit beta/CGB for choriogonadotropin. Belongs to the glycoprotein hormones subunit alpha family. Proteic grace - Issue 77 of December 2006