Purification and characterization of esterase 2B of the house mouse, Mus musculus

Esterase 2B was isolated from mouse kidney and purified about 1300-fold by ion-exchange chromatography and repeated molecular sieve chromatography. The resulting product is apparently homogeneous by the criteria of gel electrophoresis and immunodiffusion. The molecular weight was found to be 57 000. The equivalent weight (54 000) was estimated by titration of the catalytic site by bis(p-nitrophenyl) phosphate. The Km constants of seven 4-nitrophenyl esters of n-fatty acids (C2-C8) were determined. The logarithm of Km decreases linearly with increasing number of C atoms of the fatty acid moiety. Concurrently, the free enthalpy delta G'0 of the enzyme-substrate complex increases by about 2.46 kJ/mol CH2 group. Similar results are obtained when a series of esters of 8-hydroxyquinoline were used as substrates.