Application of HPLC to the Study of the Chloroplast Atpase Mg2+Dependent Mechanism

Tentoxin has at least two binding sites on CF1 and epsilon-depleted CF1 ATPases isolated from spinach chloroplast

A new procedure for synthesis of 14C-labeled tentoxin [14C-MePhe[(Z)delta]3-tentoxin], with a high specific activity, is described. Binding experiments with CF1 or CF1-epsilon isolated from spinach chloroplast have been carried out using equilibrium dialysis technique. The results show the presence of two classes of binding sites. The association constants of the two major binding sites were derived from non-linear fitting of the binding curves. At 4 degrees C, the first binding site has a value of Ka1 = 8.2 x 10(5) M(-1) in CF1 and 8.7 x 10(5) M(-1) in CF1-epsilon, while the second binding site has lower affinity with Ka2 = 1.5 x 10(4) M(-1) in CF1 and 2.3 x 10(3) M(-1) in CF1-epsilon.

The role of Mg2+ in the hydrolytic activity of the isolated chloroplast ATPase: study by high-performance liquid chromatography

The influences of total magnesium ion concentration at different total ATP concentrations, and of total ATP concentration, for different total magnesium ion concentrations, on the enzymatic rate of the isolated chloroplast F1 ATPase, have been followed by a chromatographic method consisting in the separation and determination of ADP. From the various series of curves, it is concluded that the experimental results (position of the maxima, Km values) are better fitted by a mechanism involving the activation of the enzyme by magnesium ion and hydrolysis of free ATP, rather than by the classical mechanism, for which the enzyme hydrolyzes the MgATP complex and is inhibited by Mg2+. Although the equations giving the reaction rate are similar in the two cases, the calculated values of Km are widely different. The value obtained from the classical mechanism does not agree with KD, the dissociation constant of the enzyme-substrate complex, measured by the Hummel and Dreyer method. Moreover, when the total ATP concentration tends toward the total magnesium ion concentration, the nucleotide binding to the enzyme tends toward zero, although it should be maximum if MgATP were the true substrate. Finally, the inhibitory effect of Na+ is more easily explained as a competition between this ion and the activating Mg2+, than by the classical mechanism.

Studies of the potency of protein kinase inhibitors on ATPase activities

Tyrosine as well as serine/threonine protein kinase inhibitors have potentially two sites of interaction with their targets: the protein-substrate binding site and the ATP binding site. The latter could be modelized by measuring the capacity of protein kinase inhibitors to inhibit ATPase activities. In order to do so, we assess a novel, highly sensitive HPLC method based on hydrophilic separation of [gamma-32P]ATP and [32P]Pi. The novel assay is presented. Furthermore, the potency of 13 protein kinase inhibitors was tested on two types of ATPase, namely: apyrase and partially purified liver mitochondria F1-ATPase. The method described for the assay of ATPase can be used with almost any type of enzyme catalyzing this activity. Only cibacron blue and suramin show interesting capacities in inhibiting these ATPase activities pointing out that several widely used protein kinase inhibitors are at least somewhat specific in that they do not inhibit these two ATPases.

Automated high-performance liquid chromatography of iopentol in human plasma and whole blood using on-line dialysis as sample preparation

A fully automated high-performance liquid chromatographic method has been developed for the analysis of the radiographic contrast agent iopentol in human plasma and whole blood. This method is based on on-line sample preparation with dialysis followed by pre-column enrichment of the dialysate. The method was compared with a manual sample preparation method based on protein precipitation with tetrahydrofuran. The inter-assay and intra-assay variations and the limits of quantitation were the same for both methods. The on-line combination of dialysis and column-switching high-performance liquid chromatography was shown to be a reliable and time-saving technique for monitoring iopentol in human whole blood and plasma.