Cytokine that acts as a physiological ligand for receptor tyrosine kinases LTK and ALK, leading to their activation (PubMed:26418745, PubMed:26630010, PubMed:30061385, PubMed:33411331, PubMed:34646012, PubMed:34819673). Cytokine-binding is sufficient to activate LTK (PubMed:34646012). In contrast, ALKAL2-driven activation of ALK is coupled with heparin-binding to ALK (PubMed:34646012). Stimulation of ALK signaling is involved in neural development and regulation of energy expenditure (PubMed:34646012, PubMed:34819673). Homodimer; interchain disulfide bond is not required for homodimerization. Following interaction with receptor tyrosine kinase ALK, associates with the cell membrane, membrane-binding is required to activate ALK. Widely expressed with highest levels in adrenal gland and modest levels in pancreas, testis and uterus. Belongs to the ALKAL family. It is unclear whether it activates ALK as a homodimer or a monomer (PubMed:34646012, PubMed:34819673). According to a report, homodimeric ALKAL2 activates ALK (PubMed:34819673). According to a second publication, monomeric ALKAL2 binds and activates ALK (PubMed:34646012).