Genetic analysis of human lymphocyte proteins by two-dimensional gel electrophoresis: VI. Identification of esterase D in the two-dimensional gel electrophoresis pattern of cellular proteins.

C33k polypeptide, which is a cytosol polypeptide with molecular weight of 33 000 and approximate pI value of 7.5, has three common electrophoretic phenotypes and is an abundant polypeptide in peripheral blood lymphocytes, fibroblasts and red blood cells. Family and population studies indicate that the three phenotypes of C33k polypeptide are determined by two common alleles at a single autosomal locus. The gene frequencies of the two common alleles were 0.642 and 0.358, respectively, in a Japanese population. Since esterase D has a subunit size and gene frequencies similar to those of C33k polypeptide, the phenotypes of C33k polypeptide and esterase D were compared in 18 families totaling 72 members. Perfect concordance of the phenotypes between C33k polypeptide and esterase D was observed in all 72 members. In addition, a gene dosage effect on the expression of the phenotype of C33k polypeptide was observed in the red blood cell lysate from a patient with partial 13q trisomy who was reported to have two doses of EsD1 and one dose of EsD2. These data indicate that the polymorphic C33k polypeptide is esterase D, which is assigned to chromosome 13q14. This finding is useful for the detection of proteins coding for by chromosome 13q14-linked genes in the studies on human gene mapping using somatic hybrid cell lines and two-D gel electrophoresis.