Figure 5. Comparison of low and high Ca²⁺ positions of Tm in scallop thin filament reconstructions with corresponding atomic models of vertebrate filaments.

(a, d) Surface views of vertebrate atomic models, low Ca²⁺ (magenta) and high Ca²⁺ (yellow), taken from²⁹. (b, c and e, f) Surface views of low (b, c) and high (e, f) Ca²⁺ reconstructions from Argopecten and Placopecten, respectively. (g, h and i, j) Superposition of transverse sections from low (g, h) and high (i, j) Ca²⁺ thin filament reconstructions (grey) on low Ca²⁺ (g, i; magenta) and high Ca²⁺ (h, j; yellow) atomic models. Magenta and yellow arrowheads point to Tm positions of atomic models, and grey arrowheads to Tm positions in reconstructions. Tm density in the low Ca²⁺ reconstructions is indistinguishable from that in the low Ca²⁺ model (g), but distinct from that in the high Ca²⁺ model (h); Tm density in the high Ca²⁺ reconstructions is similar to that in the high Ca²⁺ model (j), but distinct from that in the low Ca²⁺ model (i).