The Hydrodynamic Properties and Kinetic Constants with Natural Substrates of the Esterase from Malus pumila Fruit

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Abstract
An esterase (EC 3.1.1.1) from M. pumila fruit was purified to homogeneity by using ammonium sulfate precipitation, absorption on hydroxyapatite, dye Matrex affinity chromatography, S.300 Sephacryl chromatography and wide-range isoelectric focusing. Kinetic constants of these preparations were established for a series of natural ester substances. Greatest apparent affinity was for acetate esters containing 7- or 8-C skeletons and least for 4-C skeletons. The purified protein gave a relative MW of 195,000. The enzyme appears to be a tetramer of similar subunits, each with a relative MW of 50,000. Isoelectric focusing gave a single peak of activity with pI [isoelectric point] 9.33-9.66. Specific activity increased considerably from small immature fruits to large fruit at the climacteric.