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.
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Rustin et al. (1979) studied this question.
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