Bartolf M, Franson R C
Biochim Biophys Acta. 1987 Feb 14;917(2):308-17. doi: 10.1016/0005-2760(87)90135-4.
Expression of soluble, acid-active phospholipase A2 from a granule-enriched fraction of bovine adrenal medulla is modulated by adrenal medullary cytosol in an ionic strength- and pH-dependent manner. At 150 nM Na+, cytosol is inhibitory in a dose-dependent manner while at 14 and 50 mM Na+ inhibition is preceded by stimulation. The extent of inhibition increases with increasing Na+ while the extent of stimulation increases with decreasing Na+. Effects are seen primarily below pH 5. Bovine liver cytosol behaves similarly, and soluble, acid-active phospholipases A2 from bovine and rat liver are also modulated by cytosol. The predominant regulatory component has a molecular weight of 67 000 as determined by gel permeation chromatography. Serum albumin and other commercially available proteins affect expression of acid-active phospholipase A2 in a manner similar to cytosol. Acid-active phospholipase A2 activity is also present in cytosol, it is enhanced substantially upon precipitation of cytosolic proteins, and is subsequently suppressed by added protein. Modulatory effects of cytosol result from its interaction with substrate, not enzyme, but are not due to dilution of substrate by cytosolic phospholipids. The study demonstrates that proteins modulate expression of acid-active phospholipases A2 by interacting with substrate in an ionic strength- and pH-dependent fashion. Such interactions may be important in the in vivo regulation of acid-active phospholipases A2.
来自牛肾上腺髓质富含颗粒部分的可溶性酸性活性磷脂酶A2的表达受到肾上腺髓质细胞溶质的调节，这种调节依赖于离子强度和pH值。在150 nM Na+时，细胞溶质呈剂量依赖性抑制，而在14和50 mM Na+时，抑制之前会有刺激作用。抑制程度随Na+浓度增加而增加，刺激程度随Na+浓度降低而增加。主要在pH 5以下观察到这些效应。牛肝细胞溶质表现出类似的行为，牛和大鼠肝脏中的可溶性酸性活性磷脂酶A2也受到细胞溶质的调节。通过凝胶渗透色谱法测定，主要的调节成分分子量为67000。血清白蛋白和其他市售蛋白质对酸性活性磷脂酶A2表达的影响与细胞溶质类似。酸性活性磷脂酶A2活性也存在于细胞溶质中，在细胞溶质蛋白沉淀后其活性大幅增强，随后添加蛋白质会抑制其活性。细胞溶质的调节作用源于其与底物而非酶的相互作用，但并非由于细胞溶质磷脂对底物的稀释。该研究表明，蛋白质通过以离子强度和pH值依赖的方式与底物相互作用来调节酸性活性磷脂酶A2的表达。这种相互作用可能在酸性活性磷脂酶A2的体内调节中起重要作用。
