Heart 3 , 5 -cyclic phosphate diesterase

Early studies revealed that the 3, 5 -cyclic phosphate diesterase is present in all mammalian tissues (38, 33, 36), being most active in cerebral cortex (36, 37). It has also been identified in extracts of liver fluke (Fasciola hepatica), the common earthworm (Lumbricus terrestris), and fly larvae (36) and it has been studied in marine organisms (38), the cellular slime mold Dictyostelium discovdeum (39, AO), and in E. coli (Al). The enzyme has been partially purified from beef heart (30), dog heart, (A8) and bovine brain (37, A3). No highly purified preparations have yet been obtained and most studies have been performed with relatively crude preparations. 

It must be emphasized that much of the information on the enzyme to date comes from partially purified preparations. Even though it seems uniquely specific for nucleoside 3, 5 -cyclic phosphates, the possibility cannot be excluded that in some tissues more than one diesterase may be present. In fact, Hardman and Sutherland (64) have shown that a second 3, 5 -cyclic phosphate diesterase exists in heart muscle which is primarily specific for uridine 3, 5 -cyclic phosphate. This enzyme was found to be more sensitive to inhibition by theophylline and to activation by imidazole. Further studies are needed to clarify its precise status other such enzymes may be discovered in the future. 

Several analogs have been examined as substrates for nucleoside cyclic phosphate diesterase purified from a variety of tissues. In particular, Nb-monobutyryl-cAMP and DBcAMP are not hydrolyzed by cyclic nucleotide phosphodiesterase from heart 6, liver O,/ adipose tissue23,26,78 gr brain... 

Caffeine and puromycin also stimulate the conversion of phosphorylase (a) to phosphorylase (b), probably by interfering with the breakdown of the 3, 5 -cyclic adenosine nucleotide. A diesterase capable of splitting the cyclic phosphate of the 3, 5 -cyclic adenosine phosphate has been found in beef heart. The effect of epinephrine on phosphorylase is important because it constituted the first explanation of a hormone s mechanism of action in molecular terms. 

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See also in sourсe #XX -- [ , ]

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