Regulation of chicken gizzard ecto-ATPase activity by modulators that affect its oligomerization status

The major ectonucleoside triphosphate phosphohydrolase in the chicken gizza rd smooth muscle membranes is an ecto-ATPase, an integral membrane glycopro tein belonging to the E-ATPase (or E-NTPDase) family. The gizzard ecto-ATPa se is distinguished by its unusual kinetic properties, temperature dependen ce, and response to a variety of modulators. Compounds that promote oligome rization of the enzyme protein, i.e., concanavalin A, chemical cross-linkin g agent, and eosin iodoacetamide, increase its activity. Compounds that inh ibit some ion-motive ATPases, e.g., sulfhydryl reagents, xanthene derivativ es, NBD-halides, and suramin, also inhibit the gizzard ecto-ATPase, but not another E-ATPase, the chicken liver ecto-ATP-diphosphohydrolase, which con tains the same conserved regions as the ecto-ATPase. Furthermore, inhibitio n of the gizzard ecto-ATPase by these compounds as well as detergents is no t prevented by preincubation of the membranes with the substrate, ATP, indi cating that their interaction with the enzyme occurs at a locus other than the catalytic site. On the other hand, the inhibitory effect of these compo unds, except suramin, is abolished or reduced if the membranes are preincub ated with concanavalin A. It is concluded that these structurally unrelated modulators exert their effect by interfering with the oligomerization of t he ecto-ATPase protein. Our findings suggest that, under physiological cond itions, the gizzard smooth muscle ecto-ATPase may exhibit a range of activi ties determined by membrane events that affect the status of oligomerizatio n of the enzyme. (C) 2001 Academic Press.