Etherington D J
Ciba Found Symp. 1979(75):87-103. doi: 10.1002/9780470720585.ch6.
Lysosomal cathepsins B and N complete the depolymerization of native fibrillar collagen in the phagolysosome after prior extracellular fragmentation by collagenase and other neutral proteinases. In vitro studies have confirmed that cathepsins B and N cleave native collagen only at the short non-helical telopeptides, which generate the intermolecular cross-links. This action occurs maximally at pH 3.5 and at 37 degrees C the released monomers denature spontaneously and are susceptible to further breakdown. In the phagolysosome the collagenous debris is already weakened and probably therefore, more easily disrupted by these cathepsins. Complete digestion would then be undertaken by the whole complement of proteases. The lysosomal glycosidases may assist this breakdown by degrading ground substance components which are normally tightly bound to collagen. In certain situations cells may instead generate an acidic pericellular environment that could permit the direct action of secreted lysosomal enzymes. This extracellular action may supersede the action of collagenase and the activity of these different enzymes would thus be regulated by changes in the nature of this microenvironment.
在胶原酶和其他中性蛋白酶进行胞外片段化作用之后，溶酶体组织蛋白酶B和N完成吞噬溶酶体中天然纤维状胶原的解聚。体外研究证实，组织蛋白酶B和N仅在短的非螺旋端肽处切割天然胶原，这些端肽形成分子间交联。此作用在pH 3.5时最大程度发生，在37℃时释放的单体自发变性并易于进一步分解。在吞噬溶酶体中，胶原碎片已经被削弱，因此可能更容易被这些组织蛋白酶破坏。然后，整个蛋白酶补充体系会进行完全消化。溶酶体糖苷酶可能通过降解通常与胶原紧密结合的细胞外基质成分来协助这种分解。在某些情况下，细胞可能会产生酸性细胞周环境，这可以使分泌的溶酶体酶直接发挥作用。这种胞外作用可能会取代胶原酶的作用，因此这些不同酶的活性将受到这种微环境性质变化的调节。
