title: Endogenous inhibitors of cyclic adenosine 3',5'-monophosphate-phosphodiesterase in rat epididymis.
abstract: Stabilization of cyclic adenosine 3',5'-monophosphate (cAMP)-phosphodiesterase (PDE) in 50% glycerol made possible the removal of endogenous inhibitors from tissue extracts by dialysis and the storage of the extracts at -20 degrees C without loss of PDE activity. Dialysates of heat-inactivated epididymal extracts were fractionated by liquid chromatography, and 4 fractions-F2, F5, F7, and F12-were found to contain endogenous inhibitors of PDE. The masses of the fractions required to inhibit low-Km PDE activity by ca. 50% in 430-microliter incubation mixtures were F2, 89 micrograms; F5, 23 micrograms; F7, 275 micrograms; and F12, 1.2 mg. The mechanisms of inhibition of low-Km PDE by the endogenous inhibitors were investigated by kinetic analysis of enzyme-inhibitor interaction. F2 and F12 inhibited PDE competitively; F5 and F7 decreased both apparent Km and Vmax, suggesting an uncompetitive mechanism of inhibition. The high potency of F5 in low concentration suggests that it may be a physiological modulator of low-Km cAMP-PDE activity.
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors*; D000818:Animals; D004795:Enzyme Stability; D004822:Epididymis / Q000201:enzymology / Q000502:physiology*; D007700:Kinetics; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000302:isolation & purification* / Q000502:physiology; D051381:Rats
chemical_list: D010726:Phosphodiesterase Inhibitors; D015105:3',5'-Cyclic-AMP Phosphodiesterases