Purification and Properties of Aryl-α-mannosidase from Microsomal Fraction of Developing Ricinus communis Endosperms

An α-mannosidase, which would be involved in N-linked glycoprotein metabolism, was purified and characterized from microsomal fraction of developing Ricinus communis endosperms. The purified enzyme with 43 kDa on SDS-PAGE showed maximal activity at pH5.0 and 50℃, when p-nitrophenyl-α-mannopyranoside was used as a substrate. α-Mannosidase activity was inhibited by EDTA and the reduced activity was rescued by addition of Zn2+ or Ca2+, suggesting this α-mannosidase should be a metal enzyme. Ricinus aryl-α-mannosidase was able to convert the Man6GlcNAc2-PA and Man5GlcNAc2-PA to Man4GlcNAc2-PA but was completely inactive toward Man4GlcNAc2-PA, Man4Xy11GlcNAc2-PA and GlcNAc1Man5GlcNAc2-PA.