Enzyme Structure and Specific Gene Expression of Gastric Proton Pump

Abstract

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 α and glycosylated β 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 α and β subunits are closely similar to those of the corresponding subunits of Na⁺/K⁺-ATPase, suggesting that the α and β 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 α and β subunit genes. The proteins are likely to play important roles in the transcriptional regulation of the parietal cell specific genes.