Solntseva T I, Belousova A K
Biokhimiia. 1977 Jul;42(7):1331-7.
The levels of cyclic adenosine monophosphate (cAMP) and two forms of cAMP phosphodiesterase with low (PDE1) and high (PDE2) affinity for the substrate were determined in homogenates from mouse liver and transplanted hepatoma 22. The level of cAMP in the tumour is 3 times lower than that in liver. By te kinetic parameters (Vmax, Km, pH optimum) adenylate cyclase from tumour does not show any significant differences as compared to the liver enzyme; the enzyme from hepatoma is, however, more sensitive to activation by F- ions. The activities of adenylate cyclase in liver and tumour cells are the same. Phosphodiesterases of cAMP from tumour and liver cells are similar in their Km values (3,3-10(-4) M for PDE1 and 2-10(-6) M for PDE2); however, the maximal and real rates of cAMP hydrolysis in hepatoma are much higher than in liver. The fact that both cAMP phosphodiesterase activities have similar dependence on Mg2+ and Ca2+ concentrations, suggests that PDE1 is a latent form of PDE2. In tumour cells the equilibrium between these two forms is probably shifted towards the enzyme with high affinity for the substrate. The results suggest that a decreased cAMP level in hepatoma cells (as compared to the liver) is due to the activation of PDE2.
测定了小鼠肝脏匀浆和移植性肝癌22匀浆中环状单磷酸腺苷（cAMP）的水平以及对底物具有低亲和力（PDE1）和高亲和力（PDE2）的两种cAMP磷酸二酯酶的水平。肿瘤中cAMP的水平比肝脏中的低3倍。从动力学参数（Vmax、Km、最适pH）来看，肿瘤中的腺苷酸环化酶与肝脏中的酶相比没有任何显著差异；然而，肝癌中的酶对F-离子的激活更敏感。肝脏和肿瘤细胞中腺苷酸环化酶的活性相同。肿瘤细胞和肝脏细胞中cAMP的磷酸二酯酶在Km值方面相似（PDE1为3.3×10⁻⁴M，PDE2为2×10⁻⁶M）；然而，肝癌中cAMP水解的最大速率和实际速率比肝脏中的高得多。两种cAMP磷酸二酯酶活性对Mg²⁺和Ca²⁺浓度具有相似依赖性这一事实表明，PDE1是PDE2的潜在形式。在肿瘤细胞中，这两种形式之间的平衡可能向对底物具有高亲和力的酶偏移。结果表明，肝癌细胞中cAMP水平降低（与肝脏相比）是由于PDE2的激活。
