Studies on the subcellular localization of human neutrophil alkaline phosphatase

The intracellular localization of alkaline phosphatase has been determined in human neutrophils with analytical subcellular fractionation by density gradient centrifugation and EM cytochemistry. Centrifugation on sucrose gradients containing 1 mM DETA and 5 units/ml of heparin showed that alkaline phosphatase was associated with a membranous component distinct from plasma membrane, mitochondria, specific granules and azurophil granules. There was no resolution from the endoplasmic reticulum. Density gradient centrifugation on a sucrose-imidazole-heparin gradient showed a clear resolution of the alkaline phosphatase-containing membranes from the Golgi and endoplasmic reticulum. Density gradient centrifugation of neutrophils that had been disrupted in the presenceof 0.12 mmol/l. digitonin clearly separated alkaline phosphatase-containing membranes from the endoplasmic reticulum. Part of the gamma-glutamyl transferase has a similar localization to that of alkaline phosphatase. EM cytochemistry of neutrophils, neutrophil homogenates and of the density gradient fractions identified alkaline phosphatase-containing granules as irregular-shaped, often tubular, structures. It is suggested that alkaline phosphatase and part of the gamma-glutamyl transferase activity are localized to a unique organelle in the human neutrophil.