Coupling of membrane-bound and detergent-solubilized sodium- and potassium-activated ATPase to p-benzoquinone-treated microtiter plates

Effect of endothelin-1 as growth factor on a human glioma cell line; its characteristic promotion of DNA synthesis

In addition to its powerful vasoconstrictive activity, endothelin-1 (ET-1) has been recognized to stimulate DNA synthesis in some cell lines. In this study, we confirmed the existence of ET-1 receptor in YKG-1 human glioma cells, and investigated its effect on DNA synthesis in YKG-1 for 6 consecutive days, comparing it with that of epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and insulin-like growth factor-I (IGF-I). Scatchard analysis of the binding data revealed the presence of a single class of high-affinity binding molecule. The apparent dissociation constant (Kd) was 5.2 x 10(-9) M and the maximal binding capacity (B max) was 4.7 x 10(4) sites/cell. The percentage of non-cycling cells was initially more than 85%, and decreased to 55.40%, 24.22%, 11.50%, and 7.51% on days 1, 2, 4, and 6, respectively, after ET-1 stimulation. Although ET-1 reduces the fraction of non-cycling cells more slowly than other growth factors such as EGF, PDGF and IGF-I, it reaches the same level as the others by day 6. These results indicate that YKG-1 human glioma cells have ET-1 receptors and that ET-1 initiates a peculiar slow induction of DNA synthesis in these cells, suggesting that secondary factors might exist to accelerate the DNA synthesis in response to ET-1.

Directional immobilization of sodium- and potassium-activated ATPase to expose its cytoplasmic part to the liquid phase on microtiter plates by wheat germ agglutinin

A convenient method for highly efficient and directional immobilization of intact sodium- and potassium-activated ATPase (Na,K-ATPase) using wheat germ agglutinin linked on microtiter plates was developed. Wheat germ agglutinin, which bound tightly to the beta-subunit of Na,K-ATPase and had no effect on the Na,K-ATPase activity, the potassium-activated p-nitrophenylphosphatase activity, or the inhibitory action of ouabain, was covalently linked to microtiter plates and used as an immobilizer of the enzyme. The amount of Na,K-ATPase coupled to microtiter plates in this immobilizing system was more than 10-fold greater than that used in the direct immobilizing system (O. Urayama, M. Nakao, H. Nagamune, and H. Sugiyama, (1984) Anal. Biochem. 141, 194-198). Also in this system, the cytoplasmic domain of Na,K-ATPase was exposed to the liquid phase. This technique was useful for investigating the reactivities of monoclonal antibody specific for the cytoplasmic domain of the enzyme. Moreover, because this technique was used successfully in the immobilization of periodic acid--Schiff positive staining glycoprotein 1 prepared from human erythrocytes and human alpha 2-macroglobulin, the technique should also be useful for other membrane or secreted proteins that possess N-linked sugar chains containing bisecting N-acetylglucosamine or a high amount of sialic acid.