Duffy F A, Wallace A M
Department of Clinical Biochemistry, Royal Infirmary, Glasgow.
J Endocrinol. 1987 Oct;115(1):47-51. doi: 10.1677/joe.0.1150047.
The size of molecules able to be measured in immunoassays where antibody is encapsulated within semipermeable microcapsules is restricted by the pore size of the membrane. This study was performed to determine the approximate molecular weight cut-off of this membrane. Permeability was assessed by measuring which labelled hormones were able to enter and bind their respective microencapsulated antibody. Hormones with molecular weights of less than 4000 (angiotensin II, thyroxine, 17-hydroxyprogesterone, progesterone, testosterone and androstenedione) passed freely through the pores but larger molecules, with molecular weights in excess of 10,000 (parathyroid hormone, human GH, TSH) could not. Insulin, with a molecular weight of 6000 (approximate minimum diameter 3.5 nm), had restricted entry while the next smallest hormone tested, the 1-34 amino acid portion of parathyroid hormone (molecular weight 4000; diameter 1.8 nm), was able to bind encapsulated antibody, suggesting that the pore diameter is between 1.8 and 3.5 nm. It can now be predicted that the method is able to measure compounds with a diameter within this range and with a molecular weight below 6000. Microcapsules may be useful for improving specificity of assays where a cross-reactant is too large to penetrate the membrane.
在抗体被包裹于半透性微胶囊内的免疫测定中，能够被检测的分子大小受膜孔径的限制。进行本研究以确定该膜的近似分子量截留值。通过测量哪些标记激素能够进入并结合其各自的微囊化抗体来评估通透性。分子量小于4000的激素（血管紧张素II、甲状腺素、17-羟孕酮、孕酮、睾酮和雄烯二酮）可自由通过孔隙，但分子量超过10,000的较大分子（甲状旁腺激素、人生长激素、促甲状腺激素）则不能。分子量为6000（近似最小直径3.5nm）的胰岛素进入受限，而所检测的下一个最小激素，甲状旁腺激素的1-34氨基酸部分（分子量4000；直径1.8nm），能够结合微囊化抗体，这表明孔径在1.8至3.5nm之间。现在可以预测，该方法能够检测直径在此范围内且分子量低于6000的化合物。对于交叉反应物太大而无法穿透膜的测定，微胶囊可能有助于提高其特异性。
