[Comparative immunochemical characteristics of different phosphodiesterases of cyclic nucleotides].

Precipitating monospecific antibodies against purified bovine retinal rod outer segment phosphodiesterase (EC 3.1.4.17) were obtained from rabbit blood serum. These antibodies do not form precipitating complexes with phosphodiesterase isolated from rat or ox brain tissues or from the heart, lung, liver, kidney, testes and uterus of the rat. The antibodies inhibit the activity of retinal rod outer segment phosphodiesterase or that of rat brain, liver, heart and uterus enzyme (despite the lack of precipitation) but have no effect on the phosphodiesterase activity of preparations obtained from rat lungs, kidney or testes. The same effect on the phosphodiesterase activity of all these tissues is exerted by monovalent fragments of the antibodies. Using partially purified preparations of phosphodiesterase from retinal rod outer segments and brain of the ox and from human myometrium, the mechanisms of inhibition of the enzyme catalytic activity by the antibodies was studied. In the presence of the antibodies, the Km and V values appeared to be different, depending on the preparation. It was assumed that a certain site in the phosphodiesterase molecule is characterized by great structural rigidity. Taking into account the shifts in the Km values induced by the antibodies, the differences in the localization of the antigenic determinant in relation to the enzyme active center are discussed.