Sim A T, Ratcliffe E, Mumby M C, Villa-Moruzzi E, Rostas J A
Neuroscience Group, University of Newcastle, Callaghan, New South Wales, Australia.
J Neurochem. 1994 Apr;62(4):1552-9. doi: 10.1046/j.1471-4159.1994.62041552.x.
The activities and concentrations of protein phosphatase type 1 (PP1) and type 2A (PP2A) were compared in cytosol and particulate fractions of rat forebrain. Although the activity of PP2A was highest in the cytosol, immunoblot analysis with a PP2A-specific antibody showed that there were significant levels of the enzyme in the particulate fraction. There was no significant difference between the concentration of PP2A in the cytosol and particulate fractions such that the low activity of PP2A in the particulate fraction represents an inactivation of this form of the enzyme. Similar analysis in skeletal muscle, heart, and liver showed this finding was unique to the brain. Similarly, the majority of PP1 activity was recovered in the cytosol, but most PP1 enzyme was associated with the particulate fraction. Comparison with other tissues showed that the activities of PP1 in the particulate fractions were similar but that the forebrain contained significantly more enzyme than the other tissues. Thus, like PP2A it appears that the specific activity of PP1 in the particulate fraction of rat forebrain is much lower than that of the cytosol and of the particulate fractions of other tissues. Elution of PP1 and PP2A from membranes with 0.5 M NaCl plus 0.3% Triton X-100 resulted in severalfold activation of both enzymes. That the majority of PP1 and PP2A in rat forebrain are associated with membrane structures but in a low activity state suggests that novel regulatory mechanisms exist that have considerable and unique potential for activation of protein dephosphorylation.
对大鼠前脑的胞质溶胶和微粒体部分中1型蛋白磷酸酶（PP1）和2A型蛋白磷酸酶（PP2A）的活性及浓度进行了比较。虽然PP2A的活性在胞质溶胶中最高，但用PP2A特异性抗体进行的免疫印迹分析表明，微粒体部分中存在大量该酶。胞质溶胶和微粒体部分中PP2A的浓度无显著差异，因此微粒体部分中PP2A的低活性代表该形式的酶失活。在骨骼肌、心脏和肝脏中进行的类似分析表明，这一发现是大脑所特有的。同样，大部分PP1活性在胞质溶胶中检测到，但大多数PP1酶与微粒体部分相关。与其他组织的比较表明，微粒体部分中PP1的活性相似，但前脑中的酶含量明显高于其他组织。因此，与PP2A一样，大鼠前脑微粒体部分中PP1的比活性似乎远低于胞质溶胶和其他组织的微粒体部分。用0.5M NaCl加0.3% Triton X-100从膜上洗脱PP1和PP2A，可使两种酶的活性提高几倍。大鼠前脑中的大多数PP1和PP2A与膜结构相关，但处于低活性状态，这表明存在新的调节机制，具有激活蛋白质去磷酸化的巨大且独特的潜力。
