[Comparative study of cyclic nucleotide phosphodiesterase activity in the rabbit and bovine heart]. / Sravnitel'noe izuchenie aktivnosti fosfodiésterazy tsiklicheskikh nukleotidov iz serdtsa krolika i serdtsa byka.

Activities of cyclic nucleotide phosphodiesterases (PDE) were studied in partially purified preparations from bovine and rabbit heart tissues. The PDE activity from rabbit heart was not increased in the course of purification and remained distinctly lower as compared with the enzymatic activity from bovine heart. Specific chelating agent Ca2+-EGTA (5 X 10(-4)M) inhibited effectively the PDE activity from bovine heart both in the ammonium sulfate fraction and in the fractions obtained by means of gel filtration on Sepharose 6B, but affected only slightly the enzyme activity from rabbit heart. The enzyme from bovine heart appears to involve mainly the Ca2+-calmodulin -dependent form, while the enzyme from rabbit heart, isolated under similar conditions, was Ca2+-calmodulin -independent. Phenothiazine derivatives inhibited distinctly the PDE activity from bovine heart at 5 X 10(-5)M concentration, whereas they did not affect or affected only slightly the enzyme preparations from rabbit heart even at 1 X 10(-4)M concentration; the inhibition was of the calmodulin -unspecific type. Phenothiazine derivatives (inhibitors of the calmodulin activity) exhibited only slight effect on the Ca2+-calmodulin -independent PDE from rabbit heart. This enzyme could not be used in studies of drugs, the effect of which is realized via regulation of the enzymatic activity by means of Ca2+ and calmodulin.

[Some properties of partially purified preparations of cAMP phosphodiesterase from beef heart]. / Kharakteristika nekotorykh svoistv chastichno ochishchennykh preparatov fosfodiesterazy cAMP iz serdtsa byka.

Beef heart cAMP phosphodiesterase (EC 3.1.4.17) was isolated and partially purified using fractionation by ammonium sulfate and gel filtration on the columns with Sephadex G-200 and Sepharose 6B. This method allowed to preserve the enzyme binding to the low-molecular weight thermostable protein regulator of the phosphodiesterase activity. The enzyme preparation was purified 130--180-fold as compared to the original homogenate. The pH-dependence of the enzyme activity in the imidazole and tris -- buffers for the fraction with maximal activity was carried out. The kinetic analysis of this fraction revealed an abnormal kinetic behaviour with two Km values. The enzyme is represented by four forms differing in their molecular weights and possessing different capacity for activation by Ca2+ and protein regulator. No activation was observed in the forms with higher molecular weights, whereas the activity of the forms with lower molecular weights depended on the presence of Ca2+ and protein regulator. It is assumed that some of the above-described forms are capable of interconversions.