Similarities and differences between the tonoplast-type and the mitochondrial H+-ATPases of oat roots - PubMed (original) (raw)

Comparative Study

. 1985 Sep 5;260(19):10434-43.

Free article

Comparative Study

Similarities and differences between the tonoplast-type and the mitochondrial H+-ATPases of oat roots

Y Wang et al. J Biol Chem. 1985.

Free article

Abstract

The native tonoplast and the mitochondrial H+-ATPase from oat roots were compared to determine whether the two enzymes have similar mechanisms. H+ pumping in low-density microsomal vesicles reflected activity from the tonoplast-type ATPase, as ATPase activity and ATP-dependent H+ pumping (quinacrine fluorescence quenching) showed similar sensitivities to inhibition by N-ethylmaleimide, N,N'-dicyclohexylcarbodiimide, 4,4'-diisothiocyano-2,2'-stilbene disulfonate, nitrate, quercetin, or 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole. The tonoplast-type ATPase was stimulated by C1-,Br- greater than HCO3- whereas the mitochondrial ATPase was stimulated by HCO3- much greater than C1-,Br-. Both enzymes hydrolyzed ATP preferentially and were inhibited competitively by AMP or ADP. Apart from resistance to azide, the tonoplast-type ATPase was strikingly similar in its inhibitor sensitivities to the mitochondrial ATPase. The insensitivity to vanadate of both enzymes suggests the reaction mechanisms do not involve a covalent phosphoenzyme. Inhibition by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and N-ethylmaleimide and protection by ATP suggests tyrosine and cysteine residues are in the catalytic site of the tonoplast ATPase. The mitochondrial ATPase was 100 times more sensitive to N,N'-dicyclohexyl-carbodiimide inhibition than the tonoplast H+-ATPase. These results suggest the tonoplast and the mitochondrial H+-ATPases share common steps in their catalytic and vectorial reaction mechanisms, yet sufficient differences exist to indicate they are two distinct ATPases.

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