Activity and inhibitor sensitivity of ATPases in the hydrothermal vent tubeworm Riftia pachyptila:: a comparative approach

Phosphorylated ATPases may be involved in the effective pH regulation seen in the hydrothermal vent tubeworm Riftia pachyptila. R. pachyptila appears not only to have a large concentration of ATPases, but the main function of these ATPases seems to have shifted from other types of transport, such as Na+ and K+ movement, to the facilitation of Hf elimination. Plume and trophosome ATPase activity for R. pachyptila measured 646.2 +/- 29.5 and 481.4 +/- 32.0 mu mol Pi (inorganic phosphate) g(-1) wet wt h(-1), respectively. Plume tissue ATPase activity (both mass-specific and protein-specific) in R. pachyptila was higher (between 7% and 55%) than the activity measured in any tissue for 7 other shallow- and deep-living species, in this study. This supports the hypothesis that R, pachyptila regulates acid/base balance via high concentrations of H+-ATPases, including Na+/H+ and K+/H+ exchangers and possibly electrogenic H+-ATPases, as evidenced by a higher total ATPase concentration (646 mu mol Pi g(-1) wet wt h(-1)), lesser Na+/K+-ATPase activity (13% of the total, as compared to 20-40% found in other animals), and higher H+-ATPase activity (226-264 mu mol Pi g(-1) wet wt h(-1)). Overall, R. pachyptila appears to demonstrate elevated ATPase activity, with a greater fraction of the enzymes devoted to proton elimination, in order to effectively control its extracellular pH in the face of processes acting to acidify the internal environment.