Putrescine transport in human platelets.

Putrescine transport has been studied in human platelets. The uptake of putrescine is saturable and appears to be an energy-dependent process, since it is inhibited by the uncoupler 2,4-dinitrophenol and low temperature. The evidence presented suggests that the uptake process is complex and may be dependent upon pH gradient, membrane potential, and other unidentified factors. Putrescine transport is not inhibited by amino acids and is only slightly inhibited by spermidine and spermine. A membrane protein involved in putrescine transport has been identified and partially purified. Differential labeling with N-ethylmaleimide identified proteins with apparent molecular weights of 65000 and 23000 as determined by SDS-polyacrylamide gel electrophoresis. Column chromatographic purification on a putrescine affinity column revealed a Mr 55000 protein which copurified with the Mr 65000 protein. Additional evidence supporting the involvement of these proteins in putrescine transport was seen in putrescine protection against N-ethylmaleimide inhibition of putrescine uptake. Putrescine uptake may occur via the serotonin transport system, since imipramine inhibits transport and because of the similarities in the molecular weights of the proteins implicated in transport.