PTHs are found in some bacteria and some eukaryotic mitochondria.
Complete sequences are available from animals, protozoans and bacteria.
They are not found in yeast or in several bacteria for which complete genomes have been sequenced. The NAD-binding domains are homologous to those of bacterial alanine dehydrogenases and fungal saccharopine dehydrogenases. The proton-translocation pathway of the PTHs is provided by the central transmembrane domain. The membrane topology of proton-pumping Escherichia coli transhydrogenase determined by cysteine labeling. Phylogenetic analyses of proton-translocating transhydrogenases.