INHIBITION OF ANION TRANSPORT IN THE HUMAN RED-BLOOD-CELL MEMBRANE WITH PARAMETHOXYPHENYLGLYOXAL AND METAMETHOXYPHENYLGLYOXAL

The positional isomers para-methoxyphenylglyoxal and meta-methoxyphenylglyoxal were newly synthesized and found to be potent inhibitors of sulfate exchange in the red blood cell membrane. The rate of inactivation of the transport system with both reagents obeys pseudo-first-order kinetics and increases with increasing pH and reagent concentration. The degree of inhibition of the transport system with the meta-isomer exceeds the inhibition caused by the para-isomer. At 2 mM 3-methoxyphenylglyoxal (3-MOPG) and 37-degrees-C the half-lifetime of the anion transporter is 5.4 min at pH 8.0. Under the same experimental conditions the half-lifetime of the transporter at 2 mM 4-methoxyphenylglyoxal (4-MOPG) is found to be 24.7 min. The binding site of these reagents is found to be the same as binding site of the reversibly acting phenylglyoxal derivative 4-hydroxy-3-nitrophenylglyoxal (HNPG). Chloride ions are able to protect the transporter against inhibition with both reagents. Anion transport inhibitors like 4,4'-dinitrostilbene-2,2'-disulfonate (DNDS) and flufenemate, which are known to act on band 3 protein, are able to interact with the binding of the newly synthesised reagents. Phloretin and phloridzin show no interaction.