The protein phosphatases involved in cellular regulation

作者：H.Y. Lim Tung, Steven Pelech, Michael J. Fisher, Christopher I. Pogson, Philip Cohen · 发表于：European Journal of Biochemistry · 年份：1985 · DOI：10.1111/j.1432-1033.1985.tb08927.x · 被引用次数：71 · 研究领域：Polyamine Metabolism and Applications、Biochemical and Molecular Research、Ion channel regulation and function

The effects of polyamines on the oligomeric forms of protein phosphatase‐1 (1G), protein phosphatase‐2A (2A0, 2A1 and 2A2) and their free catalytic subunits (1C and 2AC) has been studied using homogeneous enzymes isolated from rabbit skeletal muscle. Spermine increased the activity of protein phosphatase‐2A towards eight of nine substrates tested. Half‐maximal activation was observed at 0.2 mM with optimal effects at 1–2 mM. Above 2 mM, spermine became inhibitory. The most impressive activation of protein phosphatase‐2A was obtained with glycogen synthase, especially when phosphorylated at sites‐3 (8–15‐fold with protein phosphatase‐2A1) and phenylalanine hydroxylase (6–7‐fold with protein phosphatase‐2A1) as substrates. Activation of protein phosphatases 2A0, 2A1 and 2A2 was greater than that observed with 2AC. Spermine was a more potent activator than spermidine, while putrescine had only a small effect. Qualitatively similar results were obtained with five other substrates, although maximal activation was much less (1.3–3‐fold with protein phosphatase‐2A1). The rate of dephosphorylation of glycogen phosphorylase was decreased by spermine, inhibition being more pronounced with protein phosphatase‐2AC than with 2A0, 2A1 and 2A2. Spermine (I50= 0.1 mM with protein phosphatase‐2AC) was a more potent inhibitor than spermidine (I50= 0.9 mM) or putrescine (I50= 8 mM). Partially purified preparations of protein phosphatases‐2A0, 2A1 and 2A2 from from rat liver were affected by spe...