Actin is one of the most abundant proteins in eukaryotic cells and is a key component of the cytoskeleton, the internal framework of the cell. Its most remarkable characteristic is its dynamic nature—it can rapidly assemble and disassemble, thereby driving cell movement and changes in cell shape.

The transforming growth factor-β (TGF-β) superfamily comprises over 30 members, including TGF-β, Activin, Inhibin, bone morphogenetic proteins (BMPs), and growth differentiation factors (GDFs). It can be roughly divided into two subfamilies: the TGF-β/Activin/Nodal subfamily and the BMP/GDF/MIS (Müllerian inhibiting substrate) subfamily.

The growth hormone (GH) family comprises pituitary GH, placental lactogens (PLs), and prolactin (PRL)—evolutionarily related hormones that signal through single-pass, class-I cytokine receptors coupled to JAK2-STAT, MAPK, and PI3K cascades.

The transforming growth factor-β (TGF-β) superfamily comprises over 30 members, including TGF-β, Activin, Inhibin, bone morphogenetic proteins (BMPs), and growth differentiation factors (GDFs). It can be roughly divided into two subfamilies: the TGF-β/Activin/Nodal subfamily and the BMP/GDF/MIS (Müllerian inhibiting substrate) subfamily.

The first discovery of fetuin-A dates back to 1944 by K. Pedersen in the blood of a fetal calf (hence the name “fetuin”) . Many years later, the independent studies by J.F. Heremans and K. Schmid with W. Burgi in 1960 and 1961, respectively, purified fetuin-A in humans, and hence it is now also known as α2-Heremans-Schmid glycoprotein (AHSG) in recognition of the discoverers.

Transferrin (TRF) is an important glycoprotein in human plasma, mainly synthesized in the liver. It is composed of 679 amino acid residues, with glycose accounting for about 6%. It has two highly homologous domains, the N - terminal and C - terminal. Each domain has a Fe³⁺ binding site and can reversibly bind two Fe³⁺.