Inhibitory Effect of Lipid Bilayer Membrane on Protein Phosphatase 2A

Protein Phosphatase 2A의 활성화에 미치는 Lipid Bilayer Membrane의 저해 효과

Protein phosphatase 2A was obtained from a cytosolic fraction of bovine brain homogenate. The phosphatase activity using phosphorylated histone Hl as substrate was suppressed in the presence of liposomes composed of dipalmitoylphosphatidylcholine(DPPC) or the mixture of phosphatidylserine and DPPC. The binding of protein phosphatase to liposome was indicated by the facts that the phosphatase activity of the supernatant of protein phosphatase/multilayer vesicle mixture was decreased with increasing amount of liposome, and that [$^{125}I$]-labeled protein phosphatase was coeluted with liposome. However, the affinity of the protein for phospholipid membrane was not so high. On the other hand, okadaic acid and liposome reduced the phosphatase activity synergistically, which means that okadaic acid binds neither to lipid membrane nor to the membrane-associated phosphatase, The inhibitory effect of liposome was, therefore, ascribed to association of the protein phosphatase 2A with the lipid bilayer membrane.

protein phosphatase 2A는 bovine brain homogenate의 세포질 fraction에서 얻어졌다. 기질로서 인산화된 histione H1을 이용하여 측정한 phosphatase 의 활성은 dipalmitoyIphophatidylcholine(DPPC) 혹은 phosphatidylserine/DPPC의 혼합물로 구성된 liposome의 존재하에서 저해되었다. Protein phosphatase 2A의 lipid membrane에의 결합은 다중층 지질막의 혼합물 계에서 liposome 의 양이 증가함에 따라서 상등액 중의 phosphatase의 활성이 감소하는 것으로 확인할 수 있었다. 또한 [$^{125}I$]protein phosphatase 2A가 liposome과 동시에 용출되는 것으로도 확인되었다. 그러나 liposome에 대한 protein phosphatase의 친화력은 높지 않았다. 한편, okadaic acid와 liposome은 협동으로 phosphatase의 활성을 감소시켰다. 이것은 okadaic acid가 lipid membrane이나 membrane에 결함한 phosphatase에는 결합하지 않는다는 것을 의미한다. 그러므로 lipid membrane에 의한 protein phosphatase 2A의 활성 저해 효과는 phosphatase 2A와 lipid membrane과의 결합에 의한 것이라고 설명될 수있다.