Exocytosis of specific granule membrane proteins

Secondary (specific) granules are peroxidase-negative and rich in antimicrobial substances (Joiner et al. 1989, Rorvig et al. 2012). They are more irregular and elongated in form than azurophil granules (Bainton et al. 1971). This may reflect volume adjustment in azurophil granules, which are known to proteolytically process a significant fraction of the proteins that are targeted to them, while little or no processing and therefore no increase in osmotic activity due to proteolysis has been observed in secondary granules (Borregaard & Cowland 1997). Secondary and tertiary granules have overlapping contents but can be discriminated by their intrinsic buoyant densities when centrifuged on gradient media (Kjeldsen et al. 1994).

次级（特定）颗粒呈过氧化物酶阴性，富含抗菌物质（Joiner 等人，1989；Rorvig 等人，2012）。其形态相较于天青颗粒更为不规则且细长（Bainton 等人，1971）。此现象可能反映了天青颗粒的体积调节，众所周知，天青颗粒通过蛋白水解作用处理了被靶向到其上的大量蛋白质，而次级颗粒则很少有或没有经过处理，因此，由于蛋白水解作用导致的渗透活性增加并未被观察到（Borregaard 与 Cowland，1997）。次级和三级颗粒内容重叠，但在梯度介质离心时，可根据其内在浮力密度进行区分（Kjeldsen 等人，1994）。