Sequential mechanism of the malonate transport system in human red blood cells

The kinetics of [2-14C] malonate transport system by the human erythrocyte membranes have been examined. The stimulation of anion- exchange band 3 protein flux could be determined by measuring [2-14C] malonate influx and efflux against its concentration gradient. The asymmetry of Km(cis), 21mM and Km(trans), 3.2 mM is of 7-fold. The Ki (cis) of malonate-malonate homoexchange was also 21mM. These results are evaluated in terms of two broad categories of kinetic models, namely ping- pong and sequential mechanisms. We conclude that anion exchange is compatible with a sequential mechanism in which a random or specific order of malonate binding sitescis & trans channel, congruently conformed asymmetrically with both inside- and outside facing orientations.
Lineweaver-Burk plots at varying [2-14C] malonate and different fixed concentrations of malonate have shown a series of interesting lines that are contrasting the other anion transport system of ping-pong mechanism. 14C-Malonate which is nonmetabolized in the erythrocyte is a useful kinetics probe for monitoring heteroexchange and self-inhibition.