Gelatinase-containing granules

The most abundant organelles within the cytoplasm are the granules, which are membrane-bound organelles containing an array of antimicrobial proteins. As discussed above ( 2.4), three major types have been identified to date azurophilic, specific and gelatinase-containing granules. Additionally, newly-described structures called secretory vesicles have been identified. 

Experiments using fluorescein-labelled fMet-Leu-Phe indicate that the majority of re-expressed receptors that appear on the plasma membrane within 4-10 min after stimulation arise from the mobilisation of internal pools. Subcellular fractionation studies indicate that the pools of these receptors are the membranes of specific granules, although it is possible that these are on other membranes (e.g. on gelatinase-containing granules or se-... 

Figure 5.7. Translocation of cytochrome b to the plasma membrane. In non-stimulated cells, only a small proportion of the total cellular pool of cytochrome b is present on the plasma membrane. The major pool of this cytochrome is located on the membranes of specific granules, gelatinase-containing granules and secretory vesicles. During activation (e.g. by fMet-Leu-Phe or PMA) or priming (e.g. by cytokines), some of these subcellular pools of cytochrome b molecules are translocated to the plasma membrane, thereby increasing the level of surface cytochrome b.

Observations of neutrophil function in whole blood and after purification have led to the realisation that many commonly-used purification procedures partially prime neutrophils, presumably by mobilising the more easily-activated subcellular stores of surface molecules (i.e. gelatinase-containing granules or secretory vesicles). 

Neutrophils possess at least four distinct types of granules (azurophil, specific, gelatinase, and secretory) which contain unique sets of polypeptides. 

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