Walter M, Plotnick M, Schechter N M
Department of Dermatology, University of Pennsylvania, Philadelphia 19104, USA.
Arch Biochem Biophys. 1996 Mar 1;327(1):81-8. doi: 10.1006/abbi.1996.0095.
The inhibition of human chymase, a chymotrypsin-like proteinase stored in mast cell granules, by secretory leukocyte proteinase inhibitor (SLPI) is investigated in this study. SLPI is a serine proteinase inhibitor present in human mucus secretions and tissues. It binds heparin, a highly sulfated glycosaminoglycan also found in mast cell secretary granules, and the interaction increases its effectiveness as an inhibitor of neutrophil elastase. Analysis of the chymase-SL interaction by equilibrium and kinetic methods indicates that the inhibition of chymase results from the reversible formation of a stable 1:1 enzyme-inhibitor complex. The dissociation equilibrium constant (determined in reactions containing 0.18 M or 1.0M NaCl (pH 8.0, 25 degrees C) was 5 X 10(-8) and 2 x 10(-8) M, respectively. Addition of heparin to the low-salt reaction decreased the Ki approximately 10-fold to a value of 3 x 10(-9) M, making SLPI a more effective inhibitor of human chymase. The decrease was due primarily to an approximately 10-fold increase in the association rate constant (kass) from 2 X 10(4) to 3 X 10(5) M-1 s-1. The magnitudes of the rate and dissociation equilibrium constants indicate that SLPI has the potential to be a good chymase inhibitor in vivo, especially if chymase and heparin are released from mast cell granules simultaneously. The enhanced interaction in the presence of heparin supports the importance of this glycosaminoglycan to the inhibitory function of SLPI.
本研究对分泌型白细胞蛋白酶抑制剂（SLPI）抑制人糜酶（一种储存于肥大细胞颗粒中的类胰凝乳蛋白酶蛋白酶）进行了研究。SLPI是一种存在于人体黏液分泌物和组织中的丝氨酸蛋白酶抑制剂。它能结合肝素（一种同样存在于肥大细胞分泌颗粒中的高度硫酸化糖胺聚糖），这种相互作用增强了其作为中性粒细胞弹性蛋白酶抑制剂的效力。通过平衡法和动力学方法对糜酶与SLPI相互作用的分析表明，糜酶的抑制作用源于稳定的1:1酶 - 抑制剂复合物的可逆形成。解离平衡常数（在含有0.18 M或1.0 M NaCl（pH 8.0，25℃）的反应中测定）分别为5×10⁻⁸和2×10⁻⁸ M。向低盐反应中添加肝素可使抑制常数（Ki）降低约10倍，至3×10⁻⁹ M，使SLPI成为人糜酶更有效的抑制剂。这种降低主要是由于缔合速率常数（kass）从2×10⁴增至3×10⁵ M⁻¹ s⁻¹，约增加了10倍。速率常数和解离平衡常数的大小表明，SLPI在体内有潜力成为一种良好的糜酶抑制剂，特别是如果糜酶和肝素同时从肥大细胞颗粒中释放出来。肝素存在时相互作用增强，支持了这种糖胺聚糖对SLPI抑制功能的重要性。
