ATPase inhibition data

Figure 4.10 Effect of reduced glutathione (GSH) (0-1.0 mM) on Na/K ATPase inhibition associated with the addition of oxidized glutathione (GSSG) (1 me). Experiments were performed using an isolated bovine ventricular Na/K ATPase preparation. Na/K ATPase activity was quantified by the ouabain-sensitive hydrolysis of ATP to yield inorganic phosphate. The data are presented as means standard errors of the means (n = 6).

Comparison of the relative carbonyl oxygen separations obtained from FITMOL with the Na+,K+-ATPase inhibition activities given in Table II revealed a striking correspondence. A simple linear regression model was used to test the relationship between oxygen separation and the I50 data for Na+,K+-ATPase... 

Figure 12. Correlation between the carbonyl oxygen separations relative to digitoxigenin, lb, and the log of the Na K+-ATPase inhibition activity (X) measured I so data (+) I50 data extrapolated from lower concentrations in which the analog was completely soluble...

The data presented here are consistent with the following structural correlations of digitalis genin-Na+,K+-ATPase inhibition ... 

In this model the unimolecular constants are relative to the turnover number and the bimolecular constants are chosen to yield equilibrium constants in units of millimolar. The model is primarily based on dead-end inhibition by CrATP, the Michaelis constant for ATP in the ATPase reaction, the isotope partitioning experiments of Rose et al. (65), and various binding and kinetic constants found in the literature. The final model was based on a computer simulation study attempting to discover what combination of rate constants would lit the isotope partition data and the observed kinetic and binding constants. 

Fig. 8. Effect of Al3+ on calcium ATPase activity (mU/mg protein) from homogenate of rat brain (panel A) and cerebellum (panel B). The inhibition by Al3+ is dose-dependent data represent the average of three independent experiments carried out in triplicate. Data are from Gandolfi et al. (1998) [31]...

An inhibition of an Mg2+ ATPase on corn root plasma membrane was also observed. Kinetic data on aluminum inhibition present a competitive pattern, as demonstrated by the Lineweaver-Burk plot with an apparent inhibition constant (K,) of 40 pM [44]. These results were obtained at pH 6.6. The authors suggested that the inhibition may be a result of either the formation of an inefficient substrate (Al-ATP) or an interaction directly with the enzyme structure. 

The isolation of the benzolactone enamide salicylihalamide A 17101 (Scheme 6.1 Part 2) was guided by the NCI s Drug Discovery Research and Development, Developmental Therapeutics Program screen for differential cytotoxicity, which showed that the Australian sample of Haliclona possessed a unique 60 cell line profile. Nanomolar potency was evident in the melanoma cell lines (GI50 = 7 nM) and a COMPARE analysis of the 60 cell line data indicated vascular ATPase (V-ATPase) activity potential. Further study of this structure class determined that salicylihalamide A is equipotent to the V-ATPase standards bafilomycin A and concanamycin A,273 but unlike these standards, selectively inhibits mammalian V-ATPases. 

Additional experiments were undertaken in which an inhibitor of myoki-nase activity was added to a similar reaction mixture. Incubations were again carried out, and samples were removed and analyzed after 20 minutes. Figure 10.5 shows profiles (three background chromatograms) in which the myokinase activity was progressively inhibited As inhibition of the myokinase increased, the amount of ADP recovered declined, and the amount of AMP increased proportionately. The area of each of the peaks (ADP and AMP) was determined, and these data (inset) illustrate the proportionality between the decline in ADP and the increase in AMP. Clearly, these results rule out the pathway for the formation of AMP from ADP, but they are consistent with the formation of ADP as a result of the combined actions of reactions (2) and (3). In addition, these data suggest that an ATPase activity is present and would account for the formation of the unlabeled ADP observed in the original experiment. 

The existing data on the effect of opiates on calmodulin and Ca + ATPase are confusing. A CDR protein isolated from heat treated synaptosomal lysates, presumably calmodulin, was found to stimulate Ca + ATPase activity. Morphine also stimulated Ca + ATPase but inhibited Ca + binding to this protein (96). It is also reported from the same laboratory that opiates inhibit Ca + ATPase activity in synaptic membranes ( 3). 

Frosolono and Pawlowski (1977) studied biochemical changes in various lung fractions prepared from rats exposed to phosgene at concentrations near to or above the LCtso. A number of enzymes showed decreased activity in all fractions these included p-nitrophenyl phosphatase, cytochrome c oxidase, ATPase and lactate dehydrogenase (LDH). The serum LDH rose. It was suggested that either inhibition of enzyme activity or loss of enzyme from cells would account for these changes. The data available did not allow... 

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