Characteristics of the cyclic AMP-phosphodiesterase activator in human brain tumours

The levels of the cyclic adenosine 3',5'-monophosphate (cyclic AMP)-phosphodiesterase (PDE) and the biochemical properties of its endogenous protein activator (PDEA) obtained from the human brain cortex and from different types of human cerebral tumours have been evaluated. The effects of the various PDEAs were studied measuring the activation of an activator-depleted cyclic AMP-PDE prepared from a normal brain cortex. The PDEA, obtained from normal and pathological tissues, did not change the affinity of the purified PDE for cyclic AMP, while it increased the Vmax of the enzyme. On the other hand, a cross-activation study showed that the PDEA lacked tissue specificity and was present in the tissue in excess over the enzyme. The levels of cyclic AMP-PDE and PDEA were much higher in normal than in tumoural tissues. The enzyme activity decreased in cerebral tumours more markedly than the protein activator. This biochemical pattern was more evident in the tumours of glial origin which are the most malignant.