The enzymatic properties of alginate lyase from Undaria pinnatifida (HARVEY) SURINGAR (Wakame) were investigated to determine how ash treatment (haiboshi) prevented texture softening. The optimum pH of the lyase was found at 7.7 and the enzyme was extremely labile for the pH values aboves 8.6. In 48-hour incubation, the lyase activity was hightest at 30°C, and completely lost by heating at 60°C for 5 min. The activity was enhanced by most bivalent metal ions, but inhibited slightly by EDTA and strongly by PCMB. The inactivation of lyase in ash-treated fronds therefore may not be due to metal ions incorporated into the fronds, but to pH values in the fronds enhanced by the ash treatment.
Kinetic examinations using the Michaelis-Menten theory for the polymannuronic acid fragmeng (SM) and for the alginate fragment of mixed uronic acid residues (SMG) suggested that a single lyase acts on both the substrates and that the enzyme may be a polymannuronic acid lyase. On the other hand, the fact that relative alginate lyase activity for polyguluronic acid fragment (SG) decrease in parallel with the algal growth suggested the existence of a polyguluronic acid lyase in this algal frond.