Strömberg K, Persson A M, Olsson I
Eur J Cell Biol. 1986 Jan;39(2):424-31.
Myeloperoxidase, stored in azurophil granules of neutrophils, is synthesized in promyelocytes as a larger molecular weight precursor, which is processed to yield a transient Mr 82 000 intermediate and mature polypeptides with molecular weights of 62 000 and 12 000. We have tried to define subcellular sites for processing using metabolic labelling of the promyelocytic leukemia cell line HL-60 in combination with subcellular fractionation on a Percoll gradient. A reasonable separation was achieved between azurophil granules, Golgi elements and endoplasmic reticulum. The finding of almost exclusively fully processed myeloperoxidase in granules and a mixture of unprocessed and processed polypeptide in fractions enriched in Golgi elements suggests that processing occurred mainly in pregranular structures. Monensin, which exchanges protons for Na+, and the base chloroquine blocked processing probably by inhibition of transport through the Golgi apparatus. However, the lysosomotropic NH4+ cation did not inhibit processing or transport indicating that processing is not necessarily influenced by pH-dependent mechanisms. Results from digestion with endoglycosidase H, incubation with tunicamycin and metabolic labelling with [3H]mannose indicated that myeloperoxidase contained high mannose oligosaccharide side chains. Also [32P]phosphate incorporated into Mr 90 000 and Mr 62 000 myeloperoxidase was susceptible to endoglycosidase H indicating that oligosaccharide side chains are modified by phosphorylation as in lysosomal enzymes. Thus, even if myeloperoxidase contained mannose 6-phosphate residues, these may not necessarily be involved in directing transport to the azurophil granules.
髓过氧化物酶储存于中性粒细胞的嗜天青颗粒中，在早幼粒细胞中作为较大分子量的前体合成，该前体经过加工产生一个瞬时的分子量为82000的中间体以及分子量为62000和12000的成熟多肽。我们试图通过早幼粒白血病细胞系HL-60的代谢标记结合在Percoll梯度上的亚细胞分级分离来确定加工的亚细胞位点。在嗜天青颗粒、高尔基体元件和内质网之间实现了合理的分离。在颗粒中几乎只发现了完全加工的髓过氧化物酶，而在富含高尔基体元件的级分中发现了未加工和已加工多肽的混合物，这表明加工主要发生在颗粒前结构中。莫能菌素可将质子与Na+交换，碱基氯喹可能通过抑制通过高尔基体的转运来阻断加工。然而，溶酶体亲和性NH4+阳离子并不抑制加工或转运，这表明加工不一定受pH依赖性机制的影响。用内切糖苷酶H消化、与衣霉素孵育以及用[3H]甘露糖进行代谢标记的结果表明，髓过氧化物酶含有高甘露糖寡糖侧链。掺入分子量为90000和62000的髓过氧化物酶中的[32P]磷酸盐也易受内切糖苷酶H的作用，这表明寡糖侧链如在溶酶体酶中一样通过磷酸化进行修饰。因此，即使髓过氧化物酶含有甘露糖6-磷酸残基，这些残基也不一定参与将其转运至嗜天青颗粒。
