Absence of the membrane marker enzyme 5′-nucleotidase in human polymorphonuclear leukocytes

As a first step in an attempt to purify the plasma membrane from human polymorphonuclear leukocytes (PMNL), we initiated a search for a marker enzyme in order to monitor the course of the purification procedure. Nucleoside-5′-monophosphatase (5′-nucleotidase) was first used as a plasma membrane marker in the isolation of this subcellular fraction from rat liver (1); it has since been described in the plasma membranes of a variety of cell types and is considered the most specific and ubiquitous enzymatic plasma membrene marker available (2). DePierre and Karnovsky have recently described 5′-nucleotidase in guinea pig peritoneal PMNL (3), and have demonstrated its existence as an ectoenzyme in a series of elegant experiments (4, 5). In contrast, the present work suggests that this enzyme is absent in the human peripheral PMNL and hydrolysis of 5′-nucleotides in this cell type is probably due to the action of nonspecific phosphatases.