PH the Hammett acidity function, "H", has been developed in connection with superacids. The concept of "unified pH scale" has been developed on the basis of the absolute chemical potential of the proton. This model uses the Lewis acid–base definition. This scale applies to liquids, gases and even solids. In 2010, a new "unified absolute pH scale" has been proposed that would allow various pH ranges across different solutions to use a common proton reference standard. Pure water is neutral. When an acid is dissolved in water, the pH will be less than 7 (25 °C). When a base, or alkali,
6TMS neutral amino acid transporter family multidrug efflux pump of the RND superfamily (TC #2.A.6.2)) and the "mar" regulon itself, and (3) MarB, a small protein of 71 amino acyl residues of unknown function. A periplasmic binding protein, MppA, essential for the uptake of the cell wall murein tripeptide, L-alanyl-γ-D-glutamyl-"meso"-diaminopimelate via the Opp permease, regulates "mar" regulon expression. Loss of MppA causes overproduction of MarA which activates "acrAB", causing pleiotropic drug resistance. MppA probably functions upstream of MarA in a signal transduction pathway that negatively controls expression of the "marRAB" operon. 6TMS neutral amino acid transporter family The 6TMS Neutral Amino Acid Transporter (NAAT) Family (TC#