Studies on human osteopontin : isolation and characterization of osteopontin in milk and serum.

Osteopontin （hereafter called as OPN）， a CaイイD12+イエD1 binding protein， has been studied as a secreted highly acidic phophoglycoprotein with diverse functions in various tissue and species。它最初是从矿物化的骨骼矩阵中分离出来的，并被研究为一个蛋白质重塑矿物化的问题。既然OPN存在于人类牛奶中，我们认为OPN在发育中的婴儿体内扮演了一个重要的角色。目前的研究目标是在人类牛奶、血清和血液细胞中分离和表征OPN，我们有来自人类牛奶的孤立性胶原蛋白，为它准备了专门的抗体，并尝试建立一个三明治型EIA系统，以确定血清中的胶原蛋白。它发现了血清骨胶原蛋白，但不是牛奶骨胶原蛋白，在与抗体的反应中显示出悖论现象，在免疫电泳中没有可检测到的抑制作用，在EIA中没有阳性反应，但在西方印迹中显示出阳性反应，在抑制测试中显示出阳性反应。将这些现象和其他循环证据纳入帐户，将其合并为血清骨蛋白具有高分子脆弱性，并将少量肽片段插入孵化时间内的少量肽。这种脆弱性，太低了，在牛奶骨胶原中也能看到。尽管如此，这种脆弱性的确切含义还没有定义，但它是可以想象的，因为OPN本身的脆弱性在其生理功能中具有一定的含义。这种可能性是在我们的实验室里进行调查的。

Osteopontin (hereafter called as OPN), a CaィイD12+ィエD1 binding protein, has been studied as a secreted highly acidic phophoglycoprotein with diverse functions in various tissue and species. It was firstly isolated from mineralized bone matrix and studied as a protein remodeling mineralized tissue. Since OPN is present in human milk, we considered that the OPN plays an important role in the osteogenesis in the developing infants. The present studies aimed to isolate and characterize OPN in human milk, serum and blood cells.We have isolated osteopontin from human milk, prepared antibodies specific for it, and tried to establish a sandwich type EIA system determining osteopontin in serum. It was found that serum osteopontin but not milk osteopontin showed paradoxical phenomena in reaction with the antibodies, making no detectable precipitation in immunoelectrophoresis and no positive reaction in EIA, but showing positive reaction in Western blot and in an inhibition tests. Taking these phenomena and other circumstantial evidences into account, it is concluded that the serum osteopontin has a high molecular fragility, fragmenting into small peptides with few epitopes during incubation time. This fragility, though much lower extent, was also seen in milk osteopontin. Although the exact casual meaning of this fragility was not defined yet, it is conceivable that the fragility of OPN itself has some meaning in its physiological functions. Such possibility is being investigated in our laboratory.