Bendtzen K
Scand J Immunol. 1978;8(1):53-61. doi: 10.1111/j.1365-3083.1978.tb00495.x.
The cyclic nucleotides guanosine 3',5'-cyclic monophosphoric acid (3',5'-cGMP) and cytidine 2',3'-cyclic monophosphoric acid (2',3'-cCMP) but not cyclic phosphodiesters derived from the bases adenine and uracil preserved LIF activity against the blocking effect of the serine protease inhibitor phenylmethylsulphonyl fluoride (PMSF). Phosphomonoesters derived from guanosine and cytidine as well as 2',3'-cGMP and 3',5'-cCMP were all inactive, indicating specificity for phosphodiester bonds and their respective positions in the two active nucleotides. The protection afforded by 3',5'-cGMP and 2',3'-cCMP was dose dependent. Thus, using 10(-3) M PMSF, 3',5'-cGMP was active at concentrations higher than 10(-5) to 10(-4) M, and 2',3'-cCMP at concentrations higher than 3 X 10(-4) to 10(-3) M. The more pronounced LIF-inhibitory effect obtained by increased concentrations of PMSF could be overcome by raising the levels of the nucleotides, indicating that the interactions between PMSF and the nucleotides with LIF were mutally exclusive. The possibility that 3',5'-cGMP and perhaps 2',3'-cCMP function as modulators of LIF is discussed, and models for the function of this lymphokine are proposed.
环核苷酸3',5'-环磷酸鸟苷（3',5'-cGMP）和2',3'-环磷酸胞苷（2',3'-cCMP），而非源自腺嘌呤和尿嘧啶碱基的环磷酸二酯，能够保留白血病抑制因子（LIF）的活性，以对抗丝氨酸蛋白酶抑制剂苯甲基磺酰氟（PMSF）的阻断作用。源自鸟苷和胞苷的磷酸单酯以及2',3'-cGMP和3',5'-cCMP均无活性，这表明对磷酸二酯键及其在两种活性核苷酸中的各自位置具有特异性。3',5'-cGMP和2',3'-cCMP提供的保护作用呈剂量依赖性。因此，使用10⁻³ M的PMSF时，3',5'-cGMP在高于10⁻⁵至10⁻⁴ M的浓度下具有活性，而2',3'-cCMP在高于3×10⁻⁴至10⁻³ M的浓度下具有活性。通过提高PMSF浓度获得的更显著的LIF抑制作用可通过提高核苷酸水平来克服，这表明PMSF与核苷酸和LIF之间的相互作用是相互排斥的。文中讨论了3',5'-cGMP以及可能的2',3'-cCMP作为LIF调节剂发挥作用的可能性，并提出了这种淋巴因子的功能模型。
