Purification and properties of an esterase B4 from human liver.

A butyryl esterase, designated B4, has been purified from human liver and some of its properties described. The activity of this enzyme comprises 0.48% of the total butyryl esterase activity found in human liver. Esterase B4 has been distinguished from other butyryl esterases by its preference for the esters of the fluorogenic compounds 4-methyl umbilliferone and fluorescein over naphthyl esters as substrates. Other distinguishing features of this esterase include a relatively high pI (pH 8.7) A monomeric structure of low molecular weight (20 000) and high solubility in solutions of ammonium sulphate.