“…The physiological significance of these receptor subtypes is still unclear . Additionally, there is a type 2 IGF-receptor (IGF-2R) with a short cytoplasmic domain lacking a tyrosine kinase harbouring a higher affinity for IGF-2 than the IGF-1R (Sakano et al 1991;Oh et al 1991;Dore, Kar, and Quirion 1997;Braulke 1999;Kiess et al 1994). This IGF-2R is a cation-independent mannose-6 phosphate (M6P) receptor binding not only IGF-2 but M6P-containing ligands.…”