| Popis: |
Actin has one high-affinity site for a divalent cation, with a Kd for Ca2+ and Mg2+ in the nanomolar range. This binding site is located at the bottom of the cleft between the two domains of the molecule (Fig. 1). The cation is coordinated not only by amino acid residues but also by the oxygen of the γ- and/or β- phosphate groups of the nucleotide, ADP or ATP respectively, which is bound further up in the cleft (Valentin-Ranc and Carlier 1989; Kabsch et al. 1990). The tightly bound cation of G-actin exchanges with other divalent cations by a simple competitive mechanism. |
