Second, even if a microbe produces collagenase and other proteases, enzymes that break down proteins, they CAN'T reach the collagen protein due to its interaction with calcium.

第二，即使微生物能产生胶原酶和其他蛋白酶，这些酶可以分解蛋白质，但由于胶原蛋白与钙的相互作用，它们无法到达胶原蛋白。

Finally, there's the tunica externa or outside tunic which is made up of loosely woven fibers of collagen protein that protect and reinforce the blood vessel and anchor it in place.

最后的外膜，由疏松结缔组织组成，含弹性纤维和胶原纤维，可保护和加固血管并使其固定。