Acetylcholinesterase in the human erythron. I. Cytochemistry

The successful demonstration and localisation of acetylcholinesterase (AChE), in cells by a cytochemical technique requires maximal expression of enzyme activity, minimal loss of AChE and precise, quantitative generation of reaction product at the actual site of the protein in vivo. These requirements are addressed in a standard technique that has been modified to avoid or optimise fixation and to exhibit enzyme activity under close-to-physiological conditions of osmolality, pH, and temperature. With these refinements and with the use of a variety of substrates and enzyme inhibitors of different specificities, true AChE was demonstrable on the membrane of erythrocytes and in the nucleus and cytoplasm of erythroblasts in bone marrow and of the constituent cells of erythroid clones in vitro. The activity in erythrocytes from umbilical cord blood was less than that in corresponding cells from the peripheral circulation of adults. AChE was observed also in human megakaryocytes and in leucocytes at all levels of differentiation, including the components of granulocyte-macrophage clones. Pseudocholinesterase was detected likewise across the spectrum of erythroid (and leucocyte) ontogeny, suggesting that these enzymes may exercise an important function in hematopoiesis.