Human tissues contain an esterase activity called ESB3, detectable by starch gel electrophoresis followed by staining with α-naphthyl butyrate. Using mononuclear leukocytes, we demonstrated an electrophoretic variant of ESB3. Family studies suggest that the variant is inherited as a simple Mendelian trait; individuals with the ESB3 2-1 phenotype are heterozygotes, designated ESB31ESB32, to distinguish them from the more common homozygotes, ESB31ESB31. The frequency of the ESB32 allele is estimated to be 0.035 in U.S. Whites. No homozygotes for this allele have yet been found.
Our studies suggest that the enzyme from ESB3 1 individuals exists primarily as a trimer of three identical subunits with a molecular weight of approximately 58000 daltons. The genetic variant (ESB32 allele) appears to be the result of a mutation that does not affect the charge of the subunit, but rather reduces its ability to form and maintain the trimeric structure.