Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Anion-sensitive ATPase

In this chapter two ATPases will be described for which a role in active transport has been assumed. The first enzyme is an anion-sensitive ATPase, which is present in many tissues and which is assumed to play a role in anion transport. The second enzyme is a K -sensitive ATPase, which has so far only been found in the gastric mucosa of several species and which seems to be involved in gastric acid secretion. The properties of these two enzymes and the evidence for their role in active transport will be described. [Pg.209]

A role of an anion-sensitive ATPase in anion transport across the plasma membrane was first suggested by Durbin and Kasbekar [3] after they found such an activity in... [Pg.209]

Subsequently, anion-sensitive ATPase activity has been demonstrated in microsomal fractions of many tissues (Table 1), in which either bicarbonate or hydrogen transport occurs, supporting a role of the enzyme in this transport. However, the fact that the ATPase of mitochondria is also anion-sensitive, has led to a debate in the literature whether there really exists a plasma membrane-bound anion-sensitive ATPase, and if so, whether this plays a role in hydrogen or bicarbonate transport (see Section 2h). [Pg.210]

We prefer to determine the enzyme activity in three media one with a stimulating anion (mostly HCO3 ), one with a neutral anion (mostly Cl ) and one with an inhibitory anion (mostly SCN ). The enzyme activity in each of these media should be given. Some authors report only the difference between a stimulating and a neutral medium whereas others give the ratio of the activities. The differential method operates on the assumption that the activity in the medium with the neutral anion is due to other ATPase activities in the enzyme preparation. The ratio method assumes that the activity in the medium with the neutral anion is completely due to a low-activity form of the anion-sensitive ATPase. Since both assumptions are contradictory and probably not true for the relatively crude enzyme preparations, it is better not to give only the difference or the ratio of the activities in these media. [Pg.210]

The preferred substrate for the anion-sensitive ATPase is ATP. The value reported for various preparations ranges from 0.1 to 0.6 mM [5,6,17,37,38]. In most experiments ATP concentrations between 2 and 5 mM have been used. Replacement of ATP by other trinucleotides generally leads to much lower enzyme activities. In... [Pg.210]

Tissues in which anion-sensitive ATPase activity has been reported... [Pg.211]

The anion-sensitive ATPase activities in brush-border preparations from rabbit kidney [17] and rat small intestine [37] have a much lower substrate specificity. In... [Pg.211]

Divalent cations are required for the anion-sensitive ATPase. The highest activity has been found with, while with Mn the activity is nearly the same in... [Pg.212]

The anion-sensitive ATPase can generally be inhibited by thiocyanate [4,5]. Since this anion inhibits gastric acid secretion, this finding has been used as an argument in favour of a role of the enzyme in proton transport. The concentration of thiocyanate required for maximal inhibition usually amounts to 5- 10 mM. The residual activity, which sometimes occurs, can be attributed to an anion-insensitive ATPase. The enzyme from brush border shows again a deviating behaviour in that it is relatively insensitive towards thiocyanate, the inhibition being less than 30% [17,37]. [Pg.213]

Fig. 1, Relationship between the relative anion affinity of anion-sensitive ATPase of lizard gastric mucosa and the relative enzyme activity in the presence of each anion alone. (From [9].)... Fig. 1, Relationship between the relative anion affinity of anion-sensitive ATPase of lizard gastric mucosa and the relative enzyme activity in the presence of each anion alone. (From [9].)...
These properties of the anion-sensitive ATPase from microsomal fractions are strikingly similar to those of the mitochondrial ATPase in several tissues [42-45]. [Pg.215]

In several tissues, like gastric mucosa [6,8,46.47], pancreas [19,20], submandibular gland [22] and intestinal mucosa [36], the anion-sensitive ATPase can be solubilized by Triton X-100, a detergent/protein ratio of 3 1 being most effective [6,8,47]. The solubihzed enzyme from gastric mucosa [46] and pancreas [20] could be partially purified by gel filtration and sucrose density gradient centrifugation. The properties of the solubilized enzyme do not differ very much from those of the particulate enzyme. [Pg.215]

Except for the inhibitory effects of thiocyanate and other anions, not many specific inhibitors have been reported. The enzyme from gastric mucosa is inhibited by OH-group-directed inhibitors, such as diisopropylfluorophosphate and methane-sulfonyl chloride and by the modifying solvent DjO [6]. Sulfhydryl reagents, like p-chloromercuribenzoate [4,20] and HgCl2 [5], inhibit the anion-sensitive ATPase from gastric mucosa and pancreas. [Pg.215]

Some studies have been carried out on the role of phosphorylated intermediates and the role of partial reactions, subunit structure and involvement of phospholipids. All these studies have been done with crude preparations from gastric mucosa, which means that the preparation contains (K -I- H )-ATPase activity (see Section 3). This makes it difficult to relate these findings to the anion-sensitive ATPase. [Pg.215]

Anion-sensitive ATPase gastric mucosa 610 gmin-fraction... [Pg.217]

The apical plasma membrane of epithelial cells of small intestinal and renal proximal tubules is characterised by the presence of many microvilli (brush border). These membranes can be isolated relatively easily by centrifugation and free flow electrophoresis techniques. Kinne-Saffran and Kinne [15] found that after free-flow electrophoresis of a rat kidney-cortex membrane preparation, the anion-sensitive ATPase co-migrated with the alkaline phosphatase activity but was separated from the (Na + K )-ATPase activity, which is assumed to be a marker of basolateral plasma membranes. This suggests that the brush-border membrane of the proximal tubule contains an anion-sensitive ATPase. The same conclusion was reached by Liang and Sacktor [17] for a brush-border preparation from rabbit kidney. [Pg.219]

The question whether or not there is an anion-sensitive ATPase in brush border membranes was reinvestigated by Kinne-Saffran and Kinne [16], They compared the properties of Mg-ATPases in a mitochondrial and a brush-border fraction from rat kidney cortex. The mitochondrial ATPase could be stimulated 90% by bicarbonate, and was very sensitive towards oligomycin, aurovertin, carboxyactryloside and the mitochondrial inhibitor protein. The brush-border Mg-ATPase could only be stimulated 28% by bicarbonate and was inhibited at most 18% by these mitochondrial inhibitors. On the other hand, the antibiotic filipin, which reacts with cholesterol in membranes, inhibits the ATPase activity in the cholesterol-rich brush-border membranes but not that in the cholesterol-poor mitochondria. The filipin treatment, however, increased the bicarbonate sensitivity of the residual ATPase activity in the brush-border preparation, suggesting that there was still some mitochondrial contamination in this preparation. [Pg.220]

In brush border of intestine also a relatively anion-insensitive ATPase could be found [37]. Previous negative findings [50] could be explained by the fact that the chelator EDTA, which inactivates this enzyme [51], was present in the incubation medium. This inactivation can be overcome by addition of excess [51]. This finding and the fact that the anion-sensitive ATPase in intestinal brush-border membranes can be inhibited by L-phenylalanine and L-cysteine suggests that the alkaline phosphatase activity and the anion-sensitive ATPase activity originates from a single enzyme [37,41]. The same conclusion has been reached for the anion-sensitive ATPase of brush border from human placenta [41], but not for the enzyme from rat kidney [16], where the alkaline phosphatase activity is inhibited by l-p-bromo-tetramisole, whereas the anion-sensitive ATPase activity is not affected. [Pg.220]

Erythrocytes do not contain mitochondria and any anion-sensitive ATPase activity in a particulate fraction must therefore be attributed to the plasma membrane. An Mg-ATPase, which could be stimulated by bicarbonate was found in rabbit erythrocyte membranes [31-33] and should thus be plasma-membrane bound. The properties of the enzyme in rabbit erythrocyte membranes are, however, completely different from those of the anion-sensitive ATPase from other tissues. Whereas sulfite is a good stimulant for the Mg-ATPase in mitochondrial and microsomal fractions of various tissues, it only slightly stimulates [32] or even inhibits [33] the erythrocyte enzyme. Other oxy-anions inhibit the ATPase of erythrocyte membranes [32]. The substrate dependence of the enzyme is greatly different from that of the enzyme from other tissues [32,33]. The half maximal inhibitory concentration of... [Pg.220]

Recent findings of Au [34] support this conclusion. He showed that erythrocyte (Ca +Mg )-ATPase and anion-sensitive ATPase activity are both stimulated by calmodulin from various sources and are inhibited by an inhibitory protein from pig erythrocytes. Also after separation of rabbit erythrocytes on the basis of their density the two activities varied in parallel in the fractions. [Pg.221]

Arguments in favour of a role of the anion-sensitive ATPase in transport are mainly based on an observed parallelism between the effect of certain inhibitors on the enzyme activity and the transport process. However, in nearly all cases the inhibitor used is the lipophilic anion thiocyanate, which might inhibit the transport process by other means. Moreover, inhibition of the mitochondrial ATPase activity led to a reduction in the amount of ATP available for other transport processes (e.g. (Na -I-K )-ATPase) causing indirect inhibition of anion transport. [Pg.221]

A prerequisite for a role of the anion-sensitive ATPase in transport would be the localisation of the enzyme in plasma membranes, since a direct role of a mitochondrial enzyme in membrane transport can be excluded. As discussed in Section 2e, it is very likely that the anion-sensitive ATPase present in microsomal fractions of various tissues from different species is due to mitochondrial contamination. [Pg.221]

In conclusion, at the moment the arguments against a role of the anion-sensitive ATPase in anion or proton transport are much stronger than those in favour of such a role. [Pg.222]

The gastric mucosa is able to generate a proton gradient of 10 1. The energy required for this transport can in principle be delivered by an ATPase and a search for such an enzyme was indicated. The earlier suggestion that a membrane-bound anion-sensitive ATPase in cooperation with carbonic anhydrase would be responsible, has been considered in Section 2 and found to be unlikely. [Pg.222]

Upon purification, the K -stimulated phosphatase activity is always copurified with the (K )-ATPase activity [63-65]. Mitochondrial markers, such as cytochrome c oxidase, succinate dehydrogenase, monoamino-oxidase, and the ribo-somal marker RNA are largely removed by the purification procedure. The same is true for the anion-sensitive ATPase and 5 nucleotidase activities, but some (Na — K )-ATPase activity is still present in highly purified (K" -I-H )-ATPase preparations. Purification is also characterised by a lowering of the K -insensitive Mg ATPase activity, but even in the purest preparations some Mg -ATPase activity (4% of (K -I- H )-ATPase activity) is still present. This may represent an impurity or an inherent property of the enzyme. [Pg.223]

The enzyme can also be inhibited by some other agents, but the mechanism of their action has not been elucidated. These agents are Zn [54,62], fluoride [54,62], vanadate [83] and dipicrylamine [66]. Other agents such as thiocyanate and ouabain, which are inhibitors of the anion-sensitive ATPase and (Na +K )-ATPase, respectively, have no effect on the (K + H )-ATPase [54], Two out of five antibody preparations against purified (K + H )-ATPase inhibit the ATPase activity for 80% and the K +-phosphatase activity for 35%, while the three other preparations have no effect on the enzyme activity [70], suggesting a heterogeneity of these preparations. [Pg.227]


See other pages where Anion-sensitive ATPase is mentioned: [Pg.209]    [Pg.209]    [Pg.211]    [Pg.211]    [Pg.212]    [Pg.215]    [Pg.216]    [Pg.216]    [Pg.216]    [Pg.217]    [Pg.218]    [Pg.219]    [Pg.219]    [Pg.219]    [Pg.221]    [Pg.221]    [Pg.227]    [Pg.229]    [Pg.231]    [Pg.233]   
See also in sourсe #XX -- [ Pg.209 , Pg.210 , Pg.211 , Pg.212 , Pg.213 , Pg.214 , Pg.215 , Pg.216 , Pg.217 , Pg.218 , Pg.219 , Pg.220 , Pg.221 ]




SEARCH



© 2024 chempedia.info