actin /ˈæktɪn/ noun2 •A globular structural protein that polymerizes in a helical fashion to form an actin filament (or microfilament).Actin has kidney-shaped polypeptide subunits, called globular actin or G actin, which bear the active sites to which the myosin heads attach during contraction. — 2012 •One of the six isoforms of actin. formsactins
