ABSTRACT
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 EDTA 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 presence of 0·12 mmol/1. digitonin clearly separated alkaline phosphatase-containing membranes from the endoplasmic reticulum. Part of the γ-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 γ-glutamyl transferase activity are localized to a unique organelle in the human neutrophil.
