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Role of membrane associated thiol groups in the functional regulation of gastric microsomal proton potassium transporting atpase system


Biochemical Journal 213(3): 587-594
Role of membrane associated thiol groups in the functional regulation of gastric microsomal proton potassium transporting atpase system
The distribution of free thiol groups associated with the membrane proteins of the purified pig gastric microsomal vesicles was quantified, and the relation of thiol groups to the function of the gastric (H+ + K+)-transporting ATPase system was investigated. Two different thiol-specific agents, carboxypyridine disulfide (CPDS) and N-(1-naphthyl)maleimide (NNM) were used for the study. The structure-function relationship of the membrane thiol groups was studied after modification by the probes under various conditions, relating the inhibition of the (H+ + K+)-transporting ATPase to the ATP-dependent H+ accumulation by the gastric microsomal vesicles. On the basis of the extent of stimulation of the microsomal (H+ + K+)-transporting ATPase in the presence and absence of valinomycin (val) .apprx. 85% of the vesicles were found to be intact. CPDS at 1 mM completely inhibits the valinomycin-stimulated ATPase and the associated p-nitrophenyl phosphatase with a concomitant inhibition of vesicular H+ uptake. Both the enzyme and dye-uptake activities were fully protected against CPDS inhibition when the treatment with CPDS was carried out in the presence of ATP. ATP also offered protection (.apprx. 65%) against NNM inhibition of the (H+ + K+)-transporting ATPase system and vesicular H+ uptake. Under similar conditions ATP also protected .apprx. 10 and 6 nmol of thiol groups/mg of protein, respectively, from CPDS and NNM reaction. The thiol groups on the outer surface of the vesicles are apparently primarily involved in gastric (H+ + K+)-transporting ATPase function. Furthermore, at least .apprx. 15% of the total microsomal thiol groups appear to be associated with the ATPase system. The data were discussed in terms of the structure-function relationship of gastric microsomes.


Accession: 006351749



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