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

An esterase (EC 3.1.1.1) from Malus pumila fruit was purified to homogeneity using ammonium sulphate precipitation, absorption on hydroxyapatite, dye Matrex affinity chromatography, S.300 Sephacryl chromatography and wide-range isoelectric focusing. 2. Kinetic constants of these preparations were established for a series of natural ester substrates. Greatest apparent affinity was for acetate esters containing seven or eight-carbon skeletons and least for four-carbon skeletons. 3. The purified protein gave a relative molecular mass of 195000. The enzyme appears to be a tetramer of similar sub-units each with a relative molecular mass of 50000 4. Isoelectric focusing gave a single peak of activity with pI 9.33-9.66. 5. Specific activity increased considerably from small immature fruits to large fruit at the climacteric.