Properties of the Endopolygalacturonase Secreted by Rhizopus stolonifer

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Abstract
SUMMARY The endopolygalacturonase secreted by Rhizopus stolonifer Ehr. ex Fr. in vivo during infection of strawberries of the cultivar ' Cambridge Favourite' was extracted with a solution of sodium chloride and partially purified by gel filtration and ion-exchange chromatography. Partial purification removed 99.8 % of the con- taminating uronide materials, but the enzyme yield was reduced to 56 % and the specific activity was increased only 2.5 times. The partially purified enzyme exhibited maximum stability at pH 4.0 to 6.0 and optimal activity at pH 4.6 to 4.8. A linear thermal-inactivation pattern between 30 and 50 "C was demonstrated and complete and irreversible inactivation was achieved by heating to 60 "C for 20 min. Enzyme activity was inhibited by 20 % or less by a range of enzyme inhibitors and cations, with 87 % inhibition occurring in the presence of IO-~ M-Hg++. The molecular weight of the enzyme was calculated as 60 000, and the sedimentation and diffusion data suggested that the enzyme molecule has a high degree of asymmetry.

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