- N N Chuang: Division of Biochemistry dand Molecular Science, Institute of Zoology, Academia Sinica, Nankang, Taipei, Taiwan, Republic of China.
A beta-mannosidase was purified ca 720-fold to homogeneity from Penaeus japonicus, with a final spec. act. of 252 U/mg of protein. 2. By using SDS-polyacrylamide gel electrophoresis, the monomers of shrimp beta-mannosidase were discovered to have mol. wts of 31,000 and those of human placental enzyme have similar mol. wts. 3.The shrimp beta-mannosidase has an isoelectric point (pI) of 5.6 +/- 0.1, and the human placental enzyme has an identical pI. Both enzymes were sialyated. 4.The shrimp beta-mannosidase has a pH optimum at 5.0 and its K(m) was 123 micrometer with 4-methylumbelliferyl-beta-D-mannopyranoside as substrate. The human enzyme has pH optimum at 4.5 and its K(m) was 10 micrometer. 5.In contrast to the discovery of thermostability with human placental beta-mannosidase, the shrimp enzyme was found to be labile to heating at 45 degree C for 20 min. Both enzyme activities were inhibited by Hg(2+) and Cd(2+) ions. However, the shrimp enzyme is significantly more sensitive to the inhibition.