Characterization of methionine transport in bovine intestinal brush border membrane vesicles

Characteristics of methionine uptake by brush border membrane vesicles of bovine small intestine were investigated. Alkaline phosphatase marked the brush border membrane fraction obtained through differential centrifugation followed by a sucrose gradient. This preparation yielded a 10-fold enrichment of activity over homogenate. Methionine uptake was found to be into an osmotically active space. A binding constant of 75.4 pmol/mg membrane protein was determined. A significant (p<.05) sodium stimulation of methionine uptake was observed. This indicated active (energy-dependent) transport in addition to the diffusive component of intravesicular mention accumulation. Decreasing the pH of buffer medium significantly (p<.05) depresses methionine transport. A K_m = .114 mM and V_MAX = 56.5 pmol/s/mg membrane protein were ascertained for methionine.