actinoid or actinide any member of the series of 15 metallic elements with proton numbers 89 (actinium) to 103 (lawrencium) inclusive that occur together in group 3 and period 7 of the IUPAC periodic table; sometimes the term is restricted to the 14 elements following actinium. Actinoid is now the preferred name. All actinoids are
actinin a minor protein constituent of muscle, found to be concentrated in both the Z line and the I band. Two components of actinin have been identified: a-actinin, F-actin cross-linking protein, a dimer of ∼200 kDa with an action similar to that of actinogelin.; and b-actinin, a dimer of ∼70 kDa, similar in action to
actin-binding protein any of several proteins that associate with either actin monomers or actin filaments in cells and modify their properties. Many of these proteins are found in the cell cortex, an actin-rich layer just below the plasma membrane. Examples include dystropin, profilin, spectrin and ankyrin, fimbrin and a-actinin (see actinin), filamin, gelsolin, and the