An unusual allantoinase from Dolichos biflorus

An unusual allantoinase from Dolichos biflorus has been purified 62-fold. The purified enzyme has an unusual pH activity profile with a shoulder at pH 4 and a peak at pH 7.5. This is due to a single enzyme which does not need metal ions for activation. In the fully reduced state the enzyme exhibits a single sharp peak at 7.5; when it is not in the sulfhydryl form (in the fully oxidized SS form?) the enzyme shows a single pH optimum at pH 4. K_m values for (±)-allantoin were 5.5 mM at pH 4 and 1.43 mM at pH 7.5. Allantoinase activity has been demonstrated in the resting seed, and increased linearly with time during the first 5 days of seedling growth.