Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.5.1.4 (deaminase)
 5,113 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Membrane-bound 3'.5'-cyclic nucleotide phosphodiesterase (EC 3.1.4.17) is closely associated physically with nucleotidase and deaminase, thus forming an enzyme cluster of unique catalytic behaviour [H. Wombacher, Archs. Biochem. Biophys. 201, 8 (1980)]. This multienzyme cluster, which was found in the microsomal fraction of beef adrenal cortex, catalyses the degradation of cyclic AMP, via AMP and adenosine, to inosine. The present study shows how theophylline, a well-known inhibitor of the phosphodiesterase, acts on the membrane-bound multienzyme sequence. The findings were as follows. Firstly, as expected, theophylline inhibited the phosphodiesterase competitively. In particular, the high-affinity enzyme was inhibited by mM concentrations of theophylline. Phosphodiesterase activity was tentatively ascribed to two enzymes, one with a low Km [0.3 microM], one with a high Km [60 microM]. Secondly, theophylline inhibited the nucleotidase activity to a great extent. A detailed kinetic analysis showed the inhibition to be hyperbolic noncompetitive (alpha = 1, beta = 0.35 and Ki = 0.25 mM). Thirdly, theophylline did not inhibit the deaminase activity of the multienzyme sequence. A model of theophylline inhibition is suggested explaining how an effector could modulate the kinetic behaviour of an enzyme cluster by acting at a single allosteric site. Finally, in view of the existence of the cyclic AMP degrading multienzyme sequence and the effect of theophylline on it, the possibility is discussed that physiologically active adenosine is derived from cyclic AMP.
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PMID:Theophylline effect on the cyclic AMP degrading multienzyme sequence. 629 12