Melloni E, Salamino F, Sparatore B, Michetti M, Pontremoli S, Horecker B L
Arch Biochem Biophys. 1984 Aug 1;232(2):513-9. doi: 10.1016/0003-9861(84)90568-x.
An endogenous inhibitor of neutral Ca2+-dependent proteinases has been isolated from rabbit liver cytosol. The inhibitor is a heat-stable, 240-kDa, tetrameric protein. It is dissociated into its 60-kDa subunits by high concentrations of Ca2+ (0.1-1 mM), but not by lower concentrations in the physiological range. Inhibition of the 150-kDa proteinase of rabbit liver [Melloni, E., Pontremoli, S., Salamino, F., Sparatore, B., Michetti, M. and Horecker, B.L. (1984) Arch. Biochem. Biophys. 232, 505-512] requires the monomeric form of the inhibitor, and occurs only at the high concentrations of Ca2+ which also cause dissociation of the dimeric 150-kDa proteinase into its 80-kDa subunits. The molecular weight of the inactive proteinase-inhibitor complex was estimated by the equilibrium gel penetration method to be 140 kDa, suggesting that it contains one subunit of proteinase and one of inhibitor. The mechanism of interaction of the inhibitor with the 200-kDa proteinase at high concentrations of Ca2+ is identical to that observed for the 150-kDa proteinase, namely dissociation of both proteinase and inhibitor into subunits and formation of an inactive 160-kDa proteinase-inhibitor complex. However, unlike the 150-kDa proteinase, which does not interact with the inhibitor at low Ca2+ concentrations, the 200-kDa proteinase is also inhibited at low concentrations of Ca2+. Under these conditions, the high-molecular-weight complex (greater than 400 kDa) formed between the tetrameric inhibitor and the dimeric proteinase prevents conversion of the 200-kDa proenzyme to the active, low-Ca2+-requiring form.
一种内源性中性钙依赖性蛋白酶抑制剂已从兔肝细胞溶胶中分离出来。该抑制剂是一种热稳定的240 kDa四聚体蛋白。高浓度的Ca2+（0.1 - 1 mM）可使其解离成60 kDa的亚基，但生理范围内的低浓度Ca2+不会使其解离。抑制兔肝150 kDa蛋白酶[梅洛尼，E.，庞特雷莫利，S.，萨拉米诺，F.，斯帕拉托雷，B.，米凯蒂，M.和霍雷克，B.L.（1984年）《生物化学与生物物理学报》232卷，505 - 512页]需要抑制剂的单体形式，且仅在高浓度Ca2+下才会发生，高浓度Ca2+还会使二聚体150 kDa蛋白酶解离成80 kDa的亚基。通过平衡凝胶渗透法估计无活性的蛋白酶 - 抑制剂复合物的分子量为140 kDa，这表明它含有一个蛋白酶亚基和一个抑制剂亚基。在高浓度Ca2+下，抑制剂与200 kDa蛋白酶相互作用的机制与150 kDa蛋白酶的情况相同，即蛋白酶和抑制剂都解离成亚基并形成无活性的160 kDa蛋白酶 - 抑制剂复合物。然而，与低Ca2+浓度下不与抑制剂相互作用得150 kDa蛋白酶不同，200 kDa蛋白酶在低浓度Ca2+下也会受到抑制。在这些条件下，四聚体抑制剂与二聚体蛋白酶之间形成的高分子量复合物（大于400 kDa）会阻止200 kDa酶原转化为需要低Ca2+的活性形式。
