Affinity-mediated membrane transport

Electrophoretic elution and "switch" monoclonal antibodies are combined in a new rapid recycle method an affinity-mediated membrane transport process reported by Dall-Bauman and Ivory (8). In this modeling paper, a "switch" monoclonal antibody incorporated into a supported liquid membrane is used to facilitate the transport of human growth hormone from a high-pH to a low-pH environment. Electrochemical effects, including Donnan equilibria between the membrane and external environments, and imposition of external electrical fields, significantly affected the flux of protein across the membrane. Experimental confirmation of the simulation results could introduce affinity-mediated transport as a powerful new biospecific separation method. 

Protein Separation via Affinity-Mediated Membrane Transport... 

Affinity-mediated transport is a form of facilitated transport in which a switch monoclonal antibody is used as a highly selective protein carrier. The membrane s physicochemical environment is controlled so that the antibody exhibits a high binding affinity for its antigen at the upstream boundary and a significantly lower binding affinity at the downstream boundary. Hence, complexation is favored upstream and decomplexation is favored downstream. 

An affinity-mediated system in which a switch monoclonal antibody is used to transport its antigen, human growth hormone, has been modeled. The affinity of the antibody for the hormone is dependent on local pH. In addition to the kinetic effect, maaoscopic and microscopic electrochemical effects were considered. On the larger scale, modest induced and applied electric fields were found to exert considerable influence on fluxes of antibody, hormone, and complexes. The short-range effect of Donnan potential was found to enhance the flux of hormone into the membrane. 

The mathematical model described here has illustrated that electrochemical effects can significantly influence protein flux in an affinity-mediated transport system. The system considered consists of a supported liquid membrane containing a pH-sensitive monoclonal antibody as carrier and human growth hormone as permeant. On a microscopic scale, Donnan inclusion of the hormone can increase the flux of hormone into the membrane. This allows more complex to be formed and simultaneously generates a steep hormone concentration gradient which drives a greater flux of free hormone than would occur in the absence of inclusion. 

Binding studies of I-labeled human transferrin to membrane preparations revealed the presence of a high affinity saturable binding site K = 2.2 x 10 m), similar to that of human transferrin receptor. Purified amastigotes of L. infantum and L. mexicana amazonensis also bind I-labeled transferrin similarly to promastigote membrane preparations. It is thus likely that transferrin mediates iron transport in both life stages of Leishmania parasites. 

Receptors located on the plasma membrane, in the cytoplasm, and in mitochondria have been described as well (36). Plasma membrane receptors are believed to mediate the transport of hormone into the cell and, possibly, to mediate nonnuclear, immediate effects of thyroid hormone (36). The presence of a large number of low-affinity cytosol binding proteins has been known for ... 

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