Subcellular distribution of glycosidases in human polymorphonuclear leucocytes

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Abstract
The subcellular distribution of nine glycosidases were studied in fractions of homogenized human polymorphonuclear leucocytes (neutrophils) obtained by isopycnic centrifugation through linear sucrose density gradients. The substrates were 4-methylumbelliferyl glycosides. All nine glycosides were hydrolysed by enzymes in neutrophil cytosol fractions, and by enzymes in at least one granule population. alpha-Glucosidase activity sedimented in sucrose density gradients to a point (p = 1.180 g/ml) just above the specific granules, possibly the ‘tertiary’ granule population. The peak corresponding to alpha-glucosidase did not co-sediment with, but considerably overlapped, the peak corresponding to lactoferrin, a marker for specific granules (p = 1.187 g/ml). alpha-Galactosidase activity was found primarily in heavy azurophil granules (p = 1.222 g/ml). alpha-Mannosidase activity was found primarily in light azurophil granules (p = 1.206 g/ml), following the distribution of myeloperoxidase, the commonly used azurophil granule marker. beta-Glucosidase activity was concentrated in mitochondrial fractions (p = 1.160 g/ml). All other glycosidases presented complex distributions, with activities not restricted to one granule class. Granule-associated glycosidase activities were increased 2–38 times when measured in the presence of 0.05% Triton X-100, indicating latency of the enzymes within granules.