Zinc Transport by Brush Border Membrane Vesicles from Rat Intestine

Abstract

Zinc uptake into isolated brush border membrane vesicles from rat intestine was investigated by using a rapid filtration technique. Uptake was saturable at 0.2 mM extravesicular zinc, while at 1.0 mM zinc uptake was nonsaturable. ATP and Na⁺ did not stimulate uptake. Some binding of zinc was noted at zero intravesicular space indicating some membrane binding may occur during transport. Initial rates of uptake were linear up to 0.3 and 0.45 mM extravesicular zinc with vesicles prepared from rats fed adequate and deficient amounts of zinc, respectively. Kinetic analysis of uptake data yielded a K_m of 0.38 mM and J_max of 5.4 nmol · minute^-1 · mg protein^-1 with vesicles from zinc-adequate rats. With vesicles from zinc-depleted rats the K_m was 0.44 mM and J_max was 12.0 nmol · minute^-1 · mg protein^-1. These uptake data suggest the brush border membrane transport system for zinc is influenced by zinc status.