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Figure 6.
Figure 6. Model of the enzymatic dissociation of
i-carrageenan fibers. A, Molecular surface of A. fortis
i-carrageenase seen from the direction opposite to the active
site groove. The surface is colored according to electrostatic
potential, ranging from + (deep blue) to - (red). The trace of a
i-carrageenan chain engaged in hydrolysis is shown as a black
line, from the reducing (R) to the non-reducing (NR) ends. B,
Model of the enzymatic dissociation of i-carrageenan
double-helix aggregates. Positive signs represent basic residues
at the outer surface of i-carrageenase. The calcium ions
coordinating the i-carrageenan double helices are shown as red
dots. We postulate that the polycationic character of the outer,
non-catalytic face of i-carrageenase is invoved with the
displacement of these calcium ions, resulting in the peeling of
the i-carrageenan fibers.
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