Bernard J P, Adrich Z, Montalto G, De Caro A, De Reggi M, Sarles H, Dagorn J C
Unité de Recherches de Physiologie et Pathologie Digestives, INSERM U 315, Marseille, France.
Gastroenterology. 1992 Oct;103(4):1277-84. doi: 10.1016/0016-5085(92)91516-7.
Pancreatic juice is naturally supersaturated in calcium and bicarbonate ions. A mechanism controlling CaCO3 crystal formation and growth is therefore necessary to prevent duct clogging. The present study shows that lithostathine, a glycoprotein present in human pancreatic juice at a concentration in the range of 10 mumol/L, could be involved in such a control. Lithostathine in concentrations greater than 1.5 mumol/L significantly delayed crystal nucleation and inhibited growth of preformed CaCO3 crystals from supersaturated solutions. Adsorption of lithostathine on crystals was shown by immunodetection. Albumin also adsorbed on CaCO3 crystals, but neither albumin nor other pancreatic secretory proteins inhibited crystal nucleation or growth. Lithostathine adsorbed to sites specifically inhibiting crystal growth with a dissociation constant (Kd) = 0.9 x 10(-6) mol/L. The glycosylated amino-terminal undecapeptide generated by limited trypsin hydrolysis inhibited CaCO3 crystal growth with a Kd = 3.0 x 10(-6) mol/L, similar to that of lithostathine. On the contrary, the carboxy-terminal polypeptide was inactive. A synthetic undecapeptide identical to the N-terminal end but not glycosylated was equally active. The activity disappeared upon digestion of the undecapeptide with V8 protease. The N-terminal undecapeptide of lithostathine is therefore essential to the inhibitory activity of the protein on CaCO3 crystal growth.
胰液天然富含钙离子和碳酸氢根离子。因此，需要一种控制碳酸钙晶体形成和生长的机制来防止导管堵塞。本研究表明，人胰液中浓度在10 μmol/L范围内的一种糖蛋白——抑石素，可能参与了这种控制。浓度大于1.5 μmol/L的抑石素显著延迟晶体成核，并抑制过饱和溶液中预先形成的碳酸钙晶体的生长。通过免疫检测显示了抑石素在晶体上的吸附。白蛋白也吸附在碳酸钙晶体上，但白蛋白和其他胰腺分泌蛋白均未抑制晶体成核或生长。抑石素吸附到特异性抑制晶体生长的位点，解离常数（Kd）= 0.9×10⁻⁶ mol/L。胰蛋白酶有限水解产生的糖基化氨基末端十一肽抑制碳酸钙晶体生长，Kd = 3.0×10⁻⁶ mol/L，与抑石素相似。相反，羧基末端多肽无活性。一种与N末端相同但未糖基化的合成十一肽同样具有活性。用V8蛋白酶消化该十一肽后活性消失。因此，抑石素的N末端十一肽对该蛋白抑制碳酸钙晶体生长的活性至关重要。
