They form reversible, stoichiometric protein-protein complexes, and play key regulatory roles in many biological processes, such as regulation of blood coagulation, the complement cascade, apoptosis, and the hormone-processing pathways. 它们按一定比例与酶结合形成可逆的蛋白质复合物,在血液凝固,补体级联反应,细胞凋亡的调控以及激素加工处理等过程中发挥重要的作用。