[Enzyme structure and specific gene expression of gastric proton pump]

Progress in molecular biological studies on the H+/K(+)-ATPase (gastric proton pump) now enables us to discuss not only its subunit protein structures and catalysis but also the organizations of its subunit genes and their cell-specific transcription. The primary structures of the catalytic alpha and glycosylated beta subunits and their transmembrane topology are similar to those of the corresponding subunits of Na+/K(+)-ATPase. The exon/intron organizations of the genes for the H+/K(+)-ATPase alpha and beta subunits are closely similar to those of the corresponding subunits of Na+/K(+)-ATPase, suggesting that the alpha and beta subunit genes of the two ATPases were respectively derived from common ancestors. In contrast to ubiquitous Na+/K(+)-ATPase, the H+/K(+)-ATPase is expressed specifically in gastric parietal cells. Consistent with this fact, we found novel zinc finger proteins which are present in the gastric parietal cells and recognize a gastric sequence motif in the 5'-upstream regions of the H+/K(+)-ATPase alpha and beta subunit genes. The proteins are likely to play important roles in the transcriptional regulation of the parietal cell specific genes.