Isolation and properties of bovine kidney brush border vacuolar H(+)-ATPase. A proton pump with enzymatic and structural differences from kidney microsomal H(+)-ATPase

Abstract

Vacuolar H(+)-ATPase was isolated from highly purified bovine kidney brush border, using a previously described immunoaffinity method. The affinity purified enzyme had reconstitutively active ATP-induced acidification that was inhibited by N-ethylmaleimide. The brush border H(+)-ATPase had a single pH optimum of 7.3, and a single Km for ATP of 360 microM. The enzyme showed no lipid activation; it had a substrate preference of ATP greater than ITP greater than UTP greater than GTP much greater than CTP, with an ATP:GTP selectivity of 1.69. The brush border H(+)-ATPase required no monovalent anion or cation for activity and was inhibited by the oxyanions NO3(-1) much greater than SO4(-2); sulfite stimulated activity at low concentrations and inhibited at higher concentrations. The inhibition produced by nitrate could not be attributed to dissociation of subunits from the enzyme. The divalent or trivalent cation preference was Mn+2 much greater than Mg+2 much greater than Co+2 greater than Al+3 greater than Ca+2 much greater than Ba+2,Sr+2; 1 mM Zn+2 inhibited the enzyme completely, but Cu+2 inhibited only 49% of activity at concentrations up to 5 mM. Sodium dodecyl sulfate-polyacrylamide gels of the brush border H(+)-ATPase showed subunits at Mr 70,000, a doublet at 56,000, 45,000, 42,000, 38,000, 33,000, 31,000, 15,000, 14,000, and 12,000. On two-dimensional gels, the pl value for the Mr 70,000 subunit was 6.3, for the Mr 56,000 was 6.4, and for the Mr 31,000 was 7.5-8.5, and microheterogeneity was observed in the Mr 56,000 and 31,000 subunits. A comparison of kidney cortex brush border H(+)-ATPase with kidney cortex microsomal H(+)-ATPase revealed differences in pH optimum, Km for ATP, lipid dependence, substrate preference, divalent ion preference, copper sensitivity, and in microheterogeneity of the Mr 56,000 and 31,000 subunits, providing evidence that different functional and structural classes of vacuolar H(+)-ATPase are segregated to specific membrane compartments.