α‐Mannosidase from Phaseolus vulgaris

A purification method for α‐mannosidase from the seeds of Phaseolus vulgaris is described. The main steps are ammonium sulfate precipitation, DEAE‐Sephadex ion‐exchange chromatography, G‐200 gel nitration, and isoelectrie focusing. Two enzymes, α‐mannosidase I and II, with isoleectric points of 5.1 and 6.1 respectively, were found. Most of the α‐mannosidase activity was present as α‐mannosidase I. This enzyme has been extensively purified. According to the criteria of disc electrophoresis and sedimentation equilibrium, the final enzyme preparation was pure. α‐Mannosidase I has a sedimentation coefficient of 11.2 S, and molecular weight of 194000. The enzyme activity was shown to depend on zinc. The pH optimum and K m value have been determined with p ‐nitrophenyl‐α‐ d ‐mannoside as substrate. α‐Mannosidase II was only partially purified and some of its properties were studied in order to compare the two enzymes.