Differences in nonspecific esterase from normal and leukemic monocytes

Nonspecific esterase (NSE) is used to identify normal and leukemic mononuclear phagocytes cytochemically. It can be demonstrated by the hydrolysis of alpha-naphthyl acetate or butyrate. NSE from leukapheresed leukemic monocytes were extracted with several types of detergent and grouped into two isoelectric point (pl) categories based on the ease of solubility: pl 5.7–6.3 (8 bands) greater than or equal to pl 6.6–7.6 (6 bands). Normal monocytes yielded only the pl 5.7–6.3 isozymes. Isozymes from both leukemic and normal monocytes were inhibited similarly by sodium fluoride, pH less than 4.7, and a serine active site inhibitor. All isozymes were bound by Sepharose- concanavalin A (Con-A) and displayed similar substrate preferences and pH v activity slopes. Under the conditions of detergent solubilization, the smallest mol wt species retaining enzymatic activity was 50 +/- 5 kd. Despite these similarities, the isozymes of pl 5.7 through 6.3 and pl greater than 6.3 exhibited different degrees or types of inhibition by phenylmethylsulfonyl fluoride (PMSF), resistance to heat and antigenic character. Thus, the esterase isozymes represent two families of glycoproteins, both of them probable cell surface enzymes, resembling classical liver carboxyl or B-esterases (EC 3.1.1 1).