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Fig. 8. Initial modulus of distal byssal threads plotted against the pH at which
they were incubated. Red dotted line and circle denote the midway point of the
Young's modulus and the corresponding pH of 6.6. The titration of a nitrogen
proton on the histidine imidazole ring (pKa=6.6) is plotted in
light gray (A/[A+AH]) to illustrate that the modulus curve closely follows the
characteristic sigmoidal shape, suggesting that histidine protonation may
influence thread mechanics. The blue inverted triangle represents the initial
stiffness of threads treated at pH 5.5 and brought back to pH 8 and tested,
indicating that pH-induced softening is reversible. The pink triangle
represents the initial stiffness of threads treated in DEPC at pH 5.5, brought
back to pH 8, and then tested. DEPC treatment further supports the role of His
in the mechanical properties of threads. Values are means ± s.e.m.;
N ranged from 6 to 9 threads for each treatment.
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