Nongastric H,K-ATPase: structure and functional properties.

Area of Science:

• Biochemistry
• Molecular Biology
• Physiology

Background:

• Nongastric H,K-ATPases, the third distinct group within the X,K-ATPase family, are encoded by ATP1AL1.
• The catalytic subunit (AL1) lacks a unique nongastric beta subunit.
• Previous studies have not identified a specific beta subunit for nongastric H,K-ATPases.

Purpose of the Study:

• To investigate the role of beta subunits in nongastric H,K-ATPase function.
• To determine the ion-transport characteristics and reaction mechanism of nongastric H,K-ATPases.
• To compare the function and properties of nongastric H,K-ATPases with Na,K-ATPases.

Main Methods:

• In situ colocalization studies in rodent prostate epithelium.
• Expression and functional analysis in Xenopus oocytes.
• Enzymatic activity assays in Sf-21 insect cells.

Main Results:

• AL1 colocalizes with and associates with beta1 of Na,K-ATPase in rodent prostate apical membranes.
• Beta1 serves as an authentic subunit for both Na,K- and nongastric H,K-pumps in this tissue.
• Human AL1 forms functional H,K-pumps with beta1NK and betaHK, exhibiting Na-dependent K-transport and a distinct reaction mechanism.
• Nongastric H,K-ATPase shows high sensitivity to bufalin, digoxin, and digitoxin, but resistance to digoxigenin and ouabagenin.

Conclusions:

• Beta1 subunit of Na,K-ATPase functions as a component of nongastric H,K-ATPase.
• Nongastric H,K-ATPase can perform Na/K-exchange, with a mechanism differing from Na,K-ATPase.
• The beta subunit does not significantly impact the ion-pump function of nongastric H,K-ATPase.