The paper reviews the current state of our knowledge on the regulation of the gastric H, K-ATPase and Kidney Na, K-ATPase activities by respective endogenous activators, HAF and the NaAF. The activators have been purified from the cytosolic fractions of the gastric and kidney tissue and partially characterized. The HAF is a dimer two identical 40 k Da subunits in the active state while the active NaAF is a monomer of 170 k Da. The gradient purified plasma membrane fractions of low and high buoyant densities derived from gastric as well as the kidney show similar kinds of stimulation by the respective activators. Also, the response of the activator stimulated activities to Ca showing abolition of the activator-stimulated component at higher physiological range was qualitatively similar for both. In addition the response to vanadate inhibition of the activator stimulated ATPase activities were virtually identical. These observations raised many questions about how the activators regulate the ATPases under physiological conditions. We have discussed these aspects under Future Direction of AF Research.

Under the Future Direction of AF Research we previously reported rapid phosphorylation of histone by the HAF, but did not understand its implication then. However, looking at a broader perspective now we believe that the HAF (and NaAF) might be auto-regulating own intra-cellular level through gene expression.