Changes in the level and activation state of the plasma membrane H+-ATPase during aging of red beet slices.

摘要

The effect of aging on the plasma membrane (PM) H+-ATPase of beetroot parenchyma discs was analysed in PM purified by aqueous two-phase partitioning. Aging increased both the activity and the amount of immunodetectable H+-ATPase in the PM. The activity assayed at slightly alkaline pH values increased earlier and more strongly than that assayed at acidic pH values, so that the pH curve of the enzyme from aged beetroot discs was shifted toward more alkaline values. Aging decreased the stimulation ofthe PM H+-ATPase activity by controlled trypsin treatments or by lysophosphatidylcholine. After trypsin treatment the pH dependence of H+-ATPase from dormant or aged beetroot discs became equal. This indicates that aging not only increases the level of H+-ATPase in the PM, but also determines its activation, most likely by modifying the interaction between the autoinhibitory carboxyl-terminal domain and the catalytic site. When the PM H+-ATPase activity was assayed at a slightly alkaline pH, the tyrosine modifier N-acetylimidazole inhibited the H+-ATPase in the PM from dormant beetroot discs much less than in the PM from aged discs, suggesting that modification of a tyrosine residue may be involved in the activation of the PM H+-ATPase induced by aging.