Shared alpha chain of heterodimeric glycoprotein hormones. These hormones bind specific receptors on target cells that in turn activate downstream signaling pathways. Involved in gametogenesis and steroidogenesis. Heterodimer. Glycoprotein hormones are heterodimers composed of a common alpha chain described here and a unique beta chain which confers their biological specificity to the different hormones. Belongs to the glycoprotein hormones subunit alpha family.