[Adventicial cyst of the popliteal artery]. / Kyste adventiciel de l'artère poplitée.

In a 42-year-old man with intermittent calf claudication, cystic adventitial disease of the popliteal artery was demonstrated by 3D CT. Cystic mass was seen to be compressing the arterial lumen. The diagnosis of cystic adventitial was confirmed by surgery. Compared with color doppler sonography, MR Imaging, 3D CT provides additional useful anatomic information concerning disease of the popliteal artery, usually gained only with sonography or arteriography.

Mediastinal bronchial artery aneurysm: dynamic computed tomography appearance.

Mediastinal aneurysms of the bronchial arteries are uncommon abnormalities with potentially fatal hemorrhagic complications. Their diagnosis is usually made by angiography in emergency situations but computed tomography (CT) scan may depict them in asymptomatic patients. We describe the CT appearance of such an aneurysm detected as an incidental finding in a patient with bleeding bronchiectasis.

Role of phosphate on the ADP-induced hysteretic inhibition of mitochondrial adenosine 5'-triphosphatase. Effects of the natural protein inhibitor.

Preincubation of F1-ATPase with ADP and Mg2+ leads to ADP binding at regulatory site inducing a hysteretic inhibition of ATP hydrolysis, i.e., an inhibition that slowly develops after Mg-ATP addition (Di Pietro, A., Penin, F., Godinot, C. and Gautheron, D.C. (1980) Biochemistry 19, 5671-5678). It is shown here that inorganic phosphate (Pi) together with ADP during preincubation abolishes the time-dependence of the inhibition after the addition of the substrate Mg-ATP. This preincubation in the presence of both Pi and ADP slowly leads to a conformation of the enzyme immediately inhibited after the addition of the substrate Mg-ATP. The Pi effect is half-maximal at 35 microM and pH 6.6, whereas a limited effect is induced at pH 8.0. The preincubation of F1-ATPase with Pi and ADP must last long enough (t1/2 = 5 min). The effects can be correlated to the amount of Pi bound to the enzyme, 1 mol Pi per mol (apparent KD of 33 microM) at saturation. Pi neither modifies the ADP binding nor the final level of the concomitant inhibition. When Pi is not present in the preincubation, the final stable rate of ADP-induced hysteretic inhibition is always reached when a near-constant amount of Pi has been generated during Mg-ATP hydrolysis. Kinetic experiments indicate that preincubation with ADP and Pi decreases both Vmax and Km which would favor a conformational change of the enzyme. Taking into account the Pi effects, a more precise model of hysteretic inhibition is proposed. The natural protein inhibitor IF1 efficiently prevents the binding of Pi produced by ATP hydrolysis indicating that the hysteretic inhibition and the IF1-dependent inhibition obey different mechanisms.

Circular dichroism and nucleotide and phosphate-induced conformational changes of mitochondrial adenosinetriphosphatase.

The conformational changes induced by the binding of different effectors on F1-ATPase are investigated by using circular dichroism and are related to enzyme activity. The hydrophilic part of the terminal enzyme of oxidative phosphorylation, F1-ATPase, solubilized from the pig heart mitochondrial membrane contains both regulatory and catalytic sites which can bind nucleotides and phosphate. The circular dichroic spectra of F1-ATPase in the absence or in the presence of ADP, Mg2+, phosphate, and the substrate analogue guanosine 5'-(beta, gamma-imidotriphosphate) [GMP-P-(NH)P] were recorded and analyzed in terms of secondary structure. The most significant result is a sizable increase from 35% to 42% of the alpha-helix content when the enzyme is incubated with all the effectors. Since the kinetic study showed that GMP-P(NH)P is a competitive inhibitor of MgATP with or without preincubation of the enzyme with ADP and phosphate, it was concluded that the catalytic and regulatory sites can be simultaneously occupied by ADP and GMP-P-(NH)P. The increase of alpha-helix content is then interpreted by a conformational change that occurs only after occupation of both types of sites.