Midkine also known as MK, MDK is a member of a small family of secreted growth factors that binds heparin and responds to retinoic acid. Midkine plays a crucial role in regulating growth and differentiation during embryogenesis, making Midkine essential for proper development. Midkine protein is primarily located in the extracellular matrix and is secreted by various cell types, which facilitates cell signaling and interaction with other growth factors. Midkine expression is tightly controlled during embryonic development, influenced by steroid receptors of the retinoic acid superfamily, and Midkine′s mature form consists of 118 amino acids with five intrachain disulfide bonds. Notably, Midkine′s carboxy-terminus harbors the principal heparin-binding site and neurite-promoting sequences, both vital for neurotrophic properties.